€•å®      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”(hhŒparent”hubaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ'/translations/zh_CN/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”(hhhh2ubah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/zh_TW/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”(hhhhFubah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/it_IT/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”(hhhhZubah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ja_JP/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”(hhhhnubah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ko_KR/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”(hhhh‚ubah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/sp_SP/staging/static-keys”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒStatic Keys”h]”hŒStatic Keys”…””}”(hhªhh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒA/var/lib/git/docbuild/linux/Documentation/staging/static-keys.rst”h KubhŒwarning”“”)”}”(hXC  DEPRECATED API:

The use of 'struct static_key' directly, is now DEPRECATED. In addition
static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following::

     struct static_key false = STATIC_KEY_INIT_FALSE;
     struct static_key true = STATIC_KEY_INIT_TRUE;
     static_key_true()
     static_key_false()

The updated API replacements are::

     DEFINE_STATIC_KEY_TRUE(key);
     DEFINE_STATIC_KEY_FALSE(key);
     DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
     DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
     static_branch_likely()
     static_branch_unlikely()”h]”(hŒ	paragraph”“”)”}”(hŒDEPRECATED API:”h]”hŒDEPRECATED API:”…””}”(hhÁhh¿hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khh¹ubh¾)”}”(hŒ“The use of 'struct static_key' directly, is now DEPRECATED. In addition
static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following::”h]”hŒ–The use of â€˜struct static_keyâ€™ directly, is now DEPRECATED. In addition
static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:”…””}”(hŒ’The use of 'struct static_key' directly, is now DEPRECATED. In addition
static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:”hhÍhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K	hh¹ubhŒliteral_block”“”)”}”(hŒ„struct static_key false = STATIC_KEY_INIT_FALSE;
struct static_key true = STATIC_KEY_INIT_TRUE;
static_key_true()
static_key_false()”h]”hŒ„struct static_key false = STATIC_KEY_INIT_FALSE;
struct static_key true = STATIC_KEY_INIT_TRUE;
static_key_true()
static_key_false()”…””}”(hhhhÞubah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1hÜhŸh¶h Khh¹ubh¾)”}”(hŒ"The updated API replacements are::”h]”hŒ!The updated API replacements are:”…””}”(hŒ!The updated API replacements are:”hhîhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khh¹ubhÝ)”}”(hŒÁDEFINE_STATIC_KEY_TRUE(key);
DEFINE_STATIC_KEY_FALSE(key);
DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
static_branch_likely()
static_branch_unlikely()”h]”hŒÁDEFINE_STATIC_KEY_TRUE(key);
DEFINE_STATIC_KEY_FALSE(key);
DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
static_branch_likely()
static_branch_unlikely()”…””}”(hhhhýubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Khh¹ubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hh£hžhhŸh¶h Nubh¢)”}”(hhh]”(h§)”}”(hŒAbstract”h]”hŒAbstract”…””}”(hj  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj  hžhhŸh¶h Kubh¾)”}”(hŒ«Static keys allows the inclusion of seldom used features in
performance-sensitive fast-path kernel code, via a GCC feature and a code
patching technique. A quick example::”h]”hŒªStatic keys allows the inclusion of seldom used features in
performance-sensitive fast-path kernel code, via a GCC feature and a code
patching technique. A quick example:”…””}”(hŒªStatic keys allows the inclusion of seldom used features in
performance-sensitive fast-path kernel code, via a GCC feature and a code
patching technique. A quick example:”hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khj  hžhubhÝ)”}”(hŒÀDEFINE_STATIC_KEY_FALSE(key);

...

if (static_branch_unlikely(&key))
        do unlikely code
else
        do likely code

...
static_branch_enable(&key);
...
static_branch_disable(&key);
...”h]”hŒÀDEFINE_STATIC_KEY_FALSE(key);

...

if (static_branch_unlikely(&key))
        do unlikely code
else
        do likely code

...
static_branch_enable(&key);
...
static_branch_disable(&key);
...”…””}”(hhhj1  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h K!hj  hžhubh¾)”}”(hŒ~The static_branch_unlikely() branch will be generated into the code with as little
impact to the likely code path as possible.”h]”hŒ~The static_branch_unlikely() branch will be generated into the code with as little
impact to the likely code path as possible.”…””}”(hjA  hj?  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K0hj  hžhubeh}”(h]”Œabstract”ah ]”h"]”Œabstract”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒ
Motivation”h]”hŒ
Motivation”…””}”(hjZ  hjX  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hjU  hžhhŸh¶h K5ubh¾)”}”(hXî  Currently, tracepoints are implemented using a conditional branch. The
conditional check requires checking a global variable for each tracepoint.
Although the overhead of this check is small, it increases when the memory
cache comes under pressure (memory cache lines for these global variables may
be shared with other memory accesses). As we increase the number of tracepoints
in the kernel this overhead may become more of an issue. In addition,
tracepoints are often dormant (disabled) and provide no direct kernel
functionality. Thus, it is highly desirable to reduce their impact as much as
possible. Although tracepoints are the original motivation for this work, other
kernel code paths should be able to make use of the static keys facility.”h]”hXî  Currently, tracepoints are implemented using a conditional branch. The
conditional check requires checking a global variable for each tracepoint.
Although the overhead of this check is small, it increases when the memory
cache comes under pressure (memory cache lines for these global variables may
be shared with other memory accesses). As we increase the number of tracepoints
in the kernel this overhead may become more of an issue. In addition,
tracepoints are often dormant (disabled) and provide no direct kernel
functionality. Thus, it is highly desirable to reduce their impact as much as
possible. Although tracepoints are the original motivation for this work, other
kernel code paths should be able to make use of the static keys facility.”…””}”(hjh  hjf  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K8hjU  hžhubeh}”(h]”Œ
motivation”ah ]”h"]”Œ
motivation”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K5ubh¢)”}”(hhh]”(h§)”}”(hŒSolution”h]”hŒSolution”…””}”(hj  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj|  hžhhŸh¶h KEubh¾)”}”(hŒLgcc (v4.5) adds a new 'asm goto' statement that allows branching to a label:”h]”hŒPgcc (v4.5) adds a new â€˜asm gotoâ€™ statement that allows branching to a label:”…””}”(hj  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KHhj|  hžhubh¾)”}”(hŒ8https://gcc.gnu.org/ml/gcc-patches/2009-07/msg01556.html”h]”hŒ	reference”“”)”}”(hj  h]”hŒ8https://gcc.gnu.org/ml/gcc-patches/2009-07/msg01556.html”…””}”(hhhj¡  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”j  uh1jŸ  hj›  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KJhj|  hžhubh¾)”}”(hŒÍUsing the 'asm goto', we can create branches that are either taken or not taken
by default, without the need to check memory. Then, at run-time, we can patch
the branch site to change the branch direction.”h]”hŒÑUsing the â€˜asm gotoâ€™, we can create branches that are either taken or not taken
by default, without the need to check memory. Then, at run-time, we can patch
the branch site to change the branch direction.”…””}”(hj·  hjµ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KLhj|  hžhubh¾)”}”(hŒEFor example, if we have a simple branch that is disabled by default::”h]”hŒDFor example, if we have a simple branch that is disabled by default:”…””}”(hŒDFor example, if we have a simple branch that is disabled by default:”hjÃ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KPhj|  hžhubhÝ)”}”(hŒKif (static_branch_unlikely(&key))
        printk("I am the true branch\n");”h]”hŒKif (static_branch_unlikely(&key))
        printk("I am the true branch\n");”…””}”(hhhjÒ  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h KRhj|  hžhubh¾)”}”(hXÇ  Thus, by default the 'printk' will not be emitted. And the code generated will
consist of a single atomic 'no-op' instruction (5 bytes on x86), in the
straight-line code path. When the branch is 'flipped', we will patch the
'no-op' in the straight-line codepath with a 'jump' instruction to the
out-of-line true branch. Thus, changing branch direction is expensive but
branch selection is basically 'free'. That is the basic tradeoff of this
optimization.”h]”hXß  Thus, by default the â€˜printkâ€™ will not be emitted. And the code generated will
consist of a single atomic â€˜no-opâ€™ instruction (5 bytes on x86), in the
straight-line code path. When the branch is â€˜flippedâ€™, we will patch the
â€˜no-opâ€™ in the straight-line codepath with a â€˜jumpâ€™ instruction to the
out-of-line true branch. Thus, changing branch direction is expensive but
branch selection is basically â€˜freeâ€™. That is the basic tradeoff of this
optimization.”…””}”(hjâ  hjà  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KUhj|  hžhubh¾)”}”(hŒvThis lowlevel patching mechanism is called 'jump label patching', and it gives
the basis for the static keys facility.”h]”hŒzThis lowlevel patching mechanism is called â€˜jump label patchingâ€™, and it gives
the basis for the static keys facility.”…””}”(hjð  hjî  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K]hj|  hžhubeh}”(h]”Œsolution”ah ]”h"]”Œsolution”ah$]”h&]”uh1h¡hh£hžhhŸh¶h KEubh¢)”}”(hhh]”(h§)”}”(hŒ(Static key label API, usage and examples”h]”hŒ(Static key label API, usage and examples”…””}”(hj	  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj  hžhhŸh¶h Kaubh¾)”}”(hŒGIn order to make use of this optimization you must first define a key::”h]”hŒFIn order to make use of this optimization you must first define a key:”…””}”(hŒFIn order to make use of this optimization you must first define a key:”hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Kdhj  hžhubhÝ)”}”(hŒDEFINE_STATIC_KEY_TRUE(key);”h]”hŒDEFINE_STATIC_KEY_TRUE(key);”…””}”(hhhj$  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kfhj  hžhubh¾)”}”(hŒor::”h]”hŒor:”…””}”(hŒor:”hj2  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khhj  hžhubhÝ)”}”(hŒDEFINE_STATIC_KEY_FALSE(key);”h]”hŒDEFINE_STATIC_KEY_FALSE(key);”…””}”(hhhjA  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kjhj  hžhubh¾)”}”(hŒiThe key must be global, that is, it can't be allocated on the stack or dynamically
allocated at run-time.”h]”hŒkThe key must be global, that is, it canâ€™t be allocated on the stack or dynamically
allocated at run-time.”…””}”(hjQ  hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Kmhj  hžhubh¾)”}”(hŒ!The key is then used in code as::”h]”hŒ The key is then used in code as:”…””}”(hŒ The key is then used in code as:”hj]  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Kphj  hžhubhÝ)”}”(hŒVif (static_branch_unlikely(&key))
        do unlikely code
else
        do likely code”h]”hŒVif (static_branch_unlikely(&key))
        do unlikely code
else
        do likely code”…””}”(hhhjl  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Krhj  hžhubh¾)”}”(hŒOr::”h]”hŒOr:”…””}”(hŒOr:”hjz  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Kwhj  hžhubhÝ)”}”(hŒTif (static_branch_likely(&key))
        do likely code
else
        do unlikely code”h]”hŒTif (static_branch_likely(&key))
        do likely code
else
        do unlikely code”…””}”(hhhj‰  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kyhj  hžhubh¾)”}”(hŒ›Keys defined via DEFINE_STATIC_KEY_TRUE(), or DEFINE_STATIC_KEY_FALSE, may
be used in either static_branch_likely() or static_branch_unlikely()
statements.”h]”hŒ›Keys defined via DEFINE_STATIC_KEY_TRUE(), or DEFINE_STATIC_KEY_FALSE, may
be used in either static_branch_likely() or static_branch_unlikely()
statements.”…””}”(hj™  hj—  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K~hj  hžhubh¾)”}”(hŒ Branch(es) can be set true via::”h]”hŒBranch(es) can be set true via:”…””}”(hŒBranch(es) can be set true via:”hj¥  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K‚hj  hžhubhÝ)”}”(hŒstatic_branch_enable(&key);”h]”hŒstatic_branch_enable(&key);”…””}”(hhhj´  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h K„hj  hžhubh¾)”}”(hŒor false via::”h]”hŒor false via:”…””}”(hŒor false via:”hjÂ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K†hj  hžhubhÝ)”}”(hŒstatic_branch_disable(&key);”h]”hŒstatic_branch_disable(&key);”…””}”(hhhjÑ  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kˆhj  hžhubh¾)”}”(hŒ:The branch(es) can then be switched via reference counts::”h]”hŒ9The branch(es) can then be switched via reference counts:”…””}”(hŒ9The branch(es) can then be switched via reference counts:”hjß  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KŠhj  hžhubhÝ)”}”(hŒ5static_branch_inc(&key);
...
static_branch_dec(&key);”h]”hŒ5static_branch_inc(&key);
...
static_branch_dec(&key);”…””}”(hhhjî  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h KŒhj  hžhubh¾)”}”(hXî  Thus, 'static_branch_inc()' means 'make the branch true', and
'static_branch_dec()' means 'make the branch false' with appropriate
reference counting. For example, if the key is initialized true, a
static_branch_dec(), will switch the branch to false. And a subsequent
static_branch_inc(), will change the branch back to true. Likewise, if the
key is initialized false, a 'static_branch_inc()', will change the branch to
true. And then a 'static_branch_dec()', will again make the branch false.”h]”hX  Thus, â€˜static_branch_inc()â€™ means â€˜make the branch trueâ€™, and
â€˜static_branch_dec()â€™ means â€˜make the branch falseâ€™ with appropriate
reference counting. For example, if the key is initialized true, a
static_branch_dec(), will switch the branch to false. And a subsequent
static_branch_inc(), will change the branch back to true. Likewise, if the
key is initialized false, a â€˜static_branch_inc()â€™, will change the branch to
true. And then a â€˜static_branch_dec()â€™, will again make the branch false.”…””}”(hjþ  hjü  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khj  hžhubh¾)”}”(hŒþThe state and the reference count can be retrieved with 'static_key_enabled()'
and 'static_key_count()'.  In general, if you use these functions, they
should be protected with the same mutex used around the enable/disable
or increment/decrement function.”h]”hX  The state and the reference count can be retrieved with â€˜static_key_enabled()â€™
and â€˜static_key_count()â€™.  In general, if you use these functions, they
should be protected with the same mutex used around the enable/disable
or increment/decrement function.”…””}”(hj  hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K˜hj  hžhubh¾)”}”(hX{  Note that switching branches results in some locks being taken,
particularly the CPU hotplug lock (in order to avoid races against
CPUs being brought in the kernel while the kernel is getting
patched). Calling the static key API from within a hotplug notifier is
thus a sure deadlock recipe. In order to still allow use of the
functionality, the following functions are provided:”h]”hX{  Note that switching branches results in some locks being taken,
particularly the CPU hotplug lock (in order to avoid races against
CPUs being brought in the kernel while the kernel is getting
patched). Calling the static key API from within a hotplug notifier is
thus a sure deadlock recipe. In order to still allow use of the
functionality, the following functions are provided:”…””}”(hj  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Khj  hžhubhŒblock_quote”“”)”}”(hhh]”h¾)”}”(hŒƒstatic_key_enable_cpuslocked()
static_key_disable_cpuslocked()
static_branch_enable_cpuslocked()
static_branch_disable_cpuslocked()”h]”hŒƒstatic_key_enable_cpuslocked()
static_key_disable_cpuslocked()
static_branch_enable_cpuslocked()
static_branch_disable_cpuslocked()”…””}”(hj-  hj+  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K¤hj(  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j&  hj  hžhhŸh¶h Nubh¾)”}”(hŒ…These functions are *not* general purpose, and must only be used when
you really know that you're in the above context, and no other.”h]”(hŒThese functions are ”…””}”(hŒThese functions are ”hj?  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ*not*”h]”hŒnot”…””}”(hhhjJ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jH  hj?  ubhŒn general purpose, and must only be used when
you really know that youâ€™re in the above context, and no other.”…””}”(hŒl general purpose, and must only be used when
you really know that you're in the above context, and no other.”hj?  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K©hj  hžhubh¾)”}”(hŒ:Where an array of keys is required, it can be defined as::”h]”hŒ9Where an array of keys is required, it can be defined as:”…””}”(hŒ9Where an array of keys is required, it can be defined as:”hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K¬hj  hžhubhÝ)”}”(hŒ*DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);”h]”hŒ*DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);”…””}”(hhhjr  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h K®hj  hžhubh¾)”}”(hŒor::”h]”hŒor:”…””}”(hŒor:”hj€  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K°hj  hžhubhÝ)”}”(hŒ+DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);”h]”hŒ+DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);”…””}”(hhhj  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h K²hj  hžhubhŒenumerated_list”“”)”}”(hhh]”hŒ	list_item”“”)”}”(hŒ;Architecture level code patching interface, 'jump labels'

”h]”h¾)”}”(hŒ9Architecture level code patching interface, 'jump labels'”h]”hŒ=Architecture level code patching interface, â€˜jump labelsâ€™”…””}”(hjª  hj¨  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K´hj¤  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjŸ  hžhhŸh¶h Nubah}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ)”Œstart”Kuh1j  hj  hžhhŸh¶h K´ubh¾)”}”(hXt  There are a few functions and macros that architectures must implement in order
to take advantage of this optimization. If there is no architecture support, we
simply fall back to a traditional, load, test, and jump sequence. Also, the
struct jump_entry table must be at least 4-byte aligned because the
static_key->entry field makes use of the two least significant bits.”h]”hXt  There are a few functions and macros that architectures must implement in order
to take advantage of this optimization. If there is no architecture support, we
simply fall back to a traditional, load, test, and jump sequence. Also, the
struct jump_entry table must be at least 4-byte aligned because the
static_key->entry field makes use of the two least significant bits.”…””}”(hjÊ  hjÈ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K·hj  hžhubhŒbullet_list”“”)”}”(hhh]”(j£  )”}”(hŒ9``select HAVE_ARCH_JUMP_LABEL``,
  see: arch/x86/Kconfig
”h]”hŒdefinition_list”“”)”}”(hhh]”hŒdefinition_list_item”“”)”}”(hŒ7``select HAVE_ARCH_JUMP_LABEL``,
see: arch/x86/Kconfig
”h]”(hŒterm”“”)”}”(hŒ ``select HAVE_ARCH_JUMP_LABEL``,”h]”(hŒliteral”“”)”}”(hŒ``select HAVE_ARCH_JUMP_LABEL``”h]”hŒselect HAVE_ARCH_JUMP_LABEL”…””}”(hhhjò  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hjì  ubhŒ,”…””}”(hŒ,”hjì  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h K¾hjæ  ubhŒ
definition”“”)”}”(hhh]”h¾)”}”(hŒsee: arch/x86/Kconfig”h]”hŒsee: arch/x86/Kconfig”…””}”(hj  hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h K¾hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjæ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h K¾hjá  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hjÛ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubj£  )”}”(hŒJ``#define JUMP_LABEL_NOP_SIZE``,
  see: arch/x86/include/asm/jump_label.h
”h]”jà  )”}”(hhh]”jå  )”}”(hŒH``#define JUMP_LABEL_NOP_SIZE``,
see: arch/x86/include/asm/jump_label.h
”h]”(jë  )”}”(hŒ ``#define JUMP_LABEL_NOP_SIZE``,”h]”(jñ  )”}”(hŒ``#define JUMP_LABEL_NOP_SIZE``”h]”hŒ#define JUMP_LABEL_NOP_SIZE”…””}”(hhhjE  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hjA  ubhŒ,”…””}”(hj  hjA  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h KÁhj=  ubj  )”}”(hhh]”h¾)”}”(hŒ&see: arch/x86/include/asm/jump_label.h”h]”hŒ&see: arch/x86/include/asm/jump_label.h”…””}”(hjb  hj`  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÁhj]  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj=  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h KÁhj:  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hj6  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubj£  )”}”(hŒ{``__always_inline bool arch_static_branch(struct static_key *key, bool branch)``,
  see: arch/x86/include/asm/jump_label.h
”h]”jà  )”}”(hhh]”jå  )”}”(hŒy``__always_inline bool arch_static_branch(struct static_key *key, bool branch)``,
see: arch/x86/include/asm/jump_label.h
”h]”(jë  )”}”(hŒQ``__always_inline bool arch_static_branch(struct static_key *key, bool branch)``,”h]”(jñ  )”}”(hŒP``__always_inline bool arch_static_branch(struct static_key *key, bool branch)``”h]”hŒL__always_inline bool arch_static_branch(struct static_key *key, bool branch)”…””}”(hhhj•  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hj‘  ubhŒ,”…””}”(hj  hj‘  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h KÄhj  ubj  )”}”(hhh]”h¾)”}”(hŒ&see: arch/x86/include/asm/jump_label.h”h]”hŒ&see: arch/x86/include/asm/jump_label.h”…””}”(hj²  hj°  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÄhj­  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h KÄhjŠ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hj†  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubj£  )”}”(hŒ€``__always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)``,
  see: arch/x86/include/asm/jump_label.h
”h]”jà  )”}”(hhh]”jå  )”}”(hŒ~``__always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)``,
see: arch/x86/include/asm/jump_label.h
”h]”(jë  )”}”(hŒV``__always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)``,”h]”(jñ  )”}”(hŒU``__always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)``”h]”hŒQ__always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)”…””}”(hhhjå  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hjá  ubhŒ,”…””}”(hj  hjá  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h KÇhjÝ  ubj  )”}”(hhh]”h¾)”}”(hŒ&see: arch/x86/include/asm/jump_label.h”h]”hŒ&see: arch/x86/include/asm/jump_label.h”…””}”(hj  hj   hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÇhjý  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjÝ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h KÇhjÚ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hjÖ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubj£  )”}”(hŒ}``void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)``,
  see: arch/x86/kernel/jump_label.c
”h]”jà  )”}”(hhh]”jå  )”}”(hŒ{``void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)``,
see: arch/x86/kernel/jump_label.c
”h]”(jë  )”}”(hŒX``void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)``,”h]”(jñ  )”}”(hŒW``void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)``”h]”hŒSvoid arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)”…””}”(hhhj5  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hj1  ubhŒ,”…””}”(hj  hj1  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h KÊhj-  ubj  )”}”(hhh]”h¾)”}”(hŒ!see: arch/x86/kernel/jump_label.c”h]”hŒ!see: arch/x86/kernel/jump_label.c”…””}”(hjR  hjP  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÊhjM  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj-  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h KÊhj*  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hj&  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubj£  )”}”(hŒA``struct jump_entry``,
  see: arch/x86/include/asm/jump_label.h

”h]”jà  )”}”(hhh]”jå  )”}”(hŒ?``struct jump_entry``,
see: arch/x86/include/asm/jump_label.h

”h]”(jë  )”}”(hŒ``struct jump_entry``,”h]”(jñ  )”}”(hŒ``struct jump_entry``”h]”hŒstruct jump_entry”…””}”(hhhj…  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jð  hj  ubhŒ,”…””}”(hj  hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1jê  hŸh¶h KÎhj}  ubj  )”}”(hhh]”h¾)”}”(hŒ&see: arch/x86/include/asm/jump_label.h”h]”hŒ&see: arch/x86/include/asm/jump_label.h”…””}”(hj¢  hj   hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÍhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj}  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jä  hŸh¶h KÎhjz  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jß  hjv  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjØ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ*”uh1jÖ  hŸh¶h K½hj  hžhubjž  )”}”(hhh]”j£  )”}”(hŒ6Static keys / jump label analysis, results (x86_64):

”h]”h¾)”}”(hŒ4Static keys / jump label analysis, results (x86_64):”h]”hŒ4Static keys / jump label analysis, results (x86_64):”…””}”(hj×  hjÕ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÐhjÑ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¢  hjÎ  hžhhŸh¶h Nubah}”(h]”h ]”h"]”h$]”h&]”jÂ  jÃ  jÄ  hjÅ  jÆ  jÇ  Kuh1j  hj  hžhhŸh¶h KÐubh¾)”}”(hŒhAs an example, let's add the following branch to 'getppid()', such that the
system call now looks like::”h]”hŒmAs an example, letâ€™s add the following branch to â€˜getppid()â€™, such that the
system call now looks like:”…””}”(hŒgAs an example, let's add the following branch to 'getppid()', such that the
system call now looks like:”hjï  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h KÓhj  hžhubhÝ)”}”(hX
  SYSCALL_DEFINE0(getppid)
{
      int pid;

+     if (static_branch_unlikely(&key))
+             printk("I am the true branch\n");

      rcu_read_lock();
      pid = task_tgid_vnr(rcu_dereference(current->real_parent));
      rcu_read_unlock();

      return pid;
}”h]”hX
  SYSCALL_DEFINE0(getppid)
{
      int pid;

+     if (static_branch_unlikely(&key))
+             printk("I am the true branch\n");

      rcu_read_lock();
      pid = task_tgid_vnr(rcu_dereference(current->real_parent));
      rcu_read_unlock();

      return pid;
}”…””}”(hhhjþ  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h KÖhj  hžhubh¾)”}”(hŒAThe resulting instructions with jump labels generated by GCC is::”h]”hŒ@The resulting instructions with jump labels generated by GCC is:”…””}”(hŒ@The resulting instructions with jump labels generated by GCC is:”hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Kähj  hžhubhÝ)”}”(hXg  ffffffff81044290 <sys_getppid>:
ffffffff81044290:       55                      push   %rbp
ffffffff81044291:       48 89 e5                mov    %rsp,%rbp
ffffffff81044294:       e9 00 00 00 00          jmpq   ffffffff81044299 <sys_getppid+0x9>
ffffffff81044299:       65 48 8b 04 25 c0 b6    mov    %gs:0xb6c0,%rax
ffffffff810442a0:       00 00
ffffffff810442a2:       48 8b 80 80 02 00 00    mov    0x280(%rax),%rax
ffffffff810442a9:       48 8b 80 b0 02 00 00    mov    0x2b0(%rax),%rax
ffffffff810442b0:       48 8b b8 e8 02 00 00    mov    0x2e8(%rax),%rdi
ffffffff810442b7:       e8 f4 d9 00 00          callq  ffffffff81051cb0 <pid_vnr>
ffffffff810442bc:       5d                      pop    %rbp
ffffffff810442bd:       48 98                   cltq
ffffffff810442bf:       c3                      retq
ffffffff810442c0:       48 c7 c7 e3 54 98 81    mov    $0xffffffff819854e3,%rdi
ffffffff810442c7:       31 c0                   xor    %eax,%eax
ffffffff810442c9:       e8 71 13 6d 00          callq  ffffffff8171563f <printk>
ffffffff810442ce:       eb c9                   jmp    ffffffff81044299 <sys_getppid+0x9>”h]”hXg  ffffffff81044290 <sys_getppid>:
ffffffff81044290:       55                      push   %rbp
ffffffff81044291:       48 89 e5                mov    %rsp,%rbp
ffffffff81044294:       e9 00 00 00 00          jmpq   ffffffff81044299 <sys_getppid+0x9>
ffffffff81044299:       65 48 8b 04 25 c0 b6    mov    %gs:0xb6c0,%rax
ffffffff810442a0:       00 00
ffffffff810442a2:       48 8b 80 80 02 00 00    mov    0x280(%rax),%rax
ffffffff810442a9:       48 8b 80 b0 02 00 00    mov    0x2b0(%rax),%rax
ffffffff810442b0:       48 8b b8 e8 02 00 00    mov    0x2e8(%rax),%rdi
ffffffff810442b7:       e8 f4 d9 00 00          callq  ffffffff81051cb0 <pid_vnr>
ffffffff810442bc:       5d                      pop    %rbp
ffffffff810442bd:       48 98                   cltq
ffffffff810442bf:       c3                      retq
ffffffff810442c0:       48 c7 c7 e3 54 98 81    mov    $0xffffffff819854e3,%rdi
ffffffff810442c7:       31 c0                   xor    %eax,%eax
ffffffff810442c9:       e8 71 13 6d 00          callq  ffffffff8171563f <printk>
ffffffff810442ce:       eb c9                   jmp    ffffffff81044299 <sys_getppid+0x9>”…””}”(hhhj  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kæhj  hžhubh¾)”}”(hŒ3Without the jump label optimization it looks like::”h]”hŒ2Without the jump label optimization it looks like:”…””}”(hŒ2Without the jump label optimization it looks like:”hj)  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Køhj  hžhubhÝ)”}”(hX‰  ffffffff810441f0 <sys_getppid>:
ffffffff810441f0:       8b 05 8a 52 d8 00       mov    0xd8528a(%rip),%eax        # ffffffff81dc9480 <key>
ffffffff810441f6:       55                      push   %rbp
ffffffff810441f7:       48 89 e5                mov    %rsp,%rbp
ffffffff810441fa:       85 c0                   test   %eax,%eax
ffffffff810441fc:       75 27                   jne    ffffffff81044225 <sys_getppid+0x35>
ffffffff810441fe:       65 48 8b 04 25 c0 b6    mov    %gs:0xb6c0,%rax
ffffffff81044205:       00 00
ffffffff81044207:       48 8b 80 80 02 00 00    mov    0x280(%rax),%rax
ffffffff8104420e:       48 8b 80 b0 02 00 00    mov    0x2b0(%rax),%rax
ffffffff81044215:       48 8b b8 e8 02 00 00    mov    0x2e8(%rax),%rdi
ffffffff8104421c:       e8 2f da 00 00          callq  ffffffff81051c50 <pid_vnr>
ffffffff81044221:       5d                      pop    %rbp
ffffffff81044222:       48 98                   cltq
ffffffff81044224:       c3                      retq
ffffffff81044225:       48 c7 c7 13 53 98 81    mov    $0xffffffff81985313,%rdi
ffffffff8104422c:       31 c0                   xor    %eax,%eax
ffffffff8104422e:       e8 60 0f 6d 00          callq  ffffffff81715193 <printk>
ffffffff81044233:       eb c9                   jmp    ffffffff810441fe <sys_getppid+0xe>
ffffffff81044235:       66 66 2e 0f 1f 84 00    data32 nopw %cs:0x0(%rax,%rax,1)
ffffffff8104423c:       00 00 00 00”h]”hX‰  ffffffff810441f0 <sys_getppid>:
ffffffff810441f0:       8b 05 8a 52 d8 00       mov    0xd8528a(%rip),%eax        # ffffffff81dc9480 <key>
ffffffff810441f6:       55                      push   %rbp
ffffffff810441f7:       48 89 e5                mov    %rsp,%rbp
ffffffff810441fa:       85 c0                   test   %eax,%eax
ffffffff810441fc:       75 27                   jne    ffffffff81044225 <sys_getppid+0x35>
ffffffff810441fe:       65 48 8b 04 25 c0 b6    mov    %gs:0xb6c0,%rax
ffffffff81044205:       00 00
ffffffff81044207:       48 8b 80 80 02 00 00    mov    0x280(%rax),%rax
ffffffff8104420e:       48 8b 80 b0 02 00 00    mov    0x2b0(%rax),%rax
ffffffff81044215:       48 8b b8 e8 02 00 00    mov    0x2e8(%rax),%rdi
ffffffff8104421c:       e8 2f da 00 00          callq  ffffffff81051c50 <pid_vnr>
ffffffff81044221:       5d                      pop    %rbp
ffffffff81044222:       48 98                   cltq
ffffffff81044224:       c3                      retq
ffffffff81044225:       48 c7 c7 13 53 98 81    mov    $0xffffffff81985313,%rdi
ffffffff8104422c:       31 c0                   xor    %eax,%eax
ffffffff8104422e:       e8 60 0f 6d 00          callq  ffffffff81715193 <printk>
ffffffff81044233:       eb c9                   jmp    ffffffff810441fe <sys_getppid+0xe>
ffffffff81044235:       66 66 2e 0f 1f 84 00    data32 nopw %cs:0x0(%rax,%rax,1)
ffffffff8104423c:       00 00 00 00”…””}”(hhhj8  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Kúhj  hžhubh¾)”}”(hŒøThus, the disable jump label case adds a 'mov', 'test' and 'jne' instruction
vs. the jump label case just has a 'no-op' or 'jmp 0'. (The jmp 0, is patched
to a 5 byte atomic no-op instruction at boot-time.) Thus, the disabled jump
label case adds::”h]”hX  Thus, the disable jump label case adds a â€˜movâ€™, â€˜testâ€™ and â€˜jneâ€™ instruction
vs. the jump label case just has a â€˜no-opâ€™ or â€˜jmp 0â€™. (The jmp 0, is patched
to a 5 byte atomic no-op instruction at boot-time.) Thus, the disabled jump
label case adds:”…””}”(hŒ÷Thus, the disable jump label case adds a 'mov', 'test' and 'jne' instruction
vs. the jump label case just has a 'no-op' or 'jmp 0'. (The jmp 0, is patched
to a 5 byte atomic no-op instruction at boot-time.) Thus, the disabled jump
label case adds:”hjF  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Mhj  hžhubhÝ)”}”(hŒI6 (mov) + 2 (test) + 2 (jne) = 10 - 5 (5 byte jump 0) = 5 addition bytes.”h]”hŒI6 (mov) + 2 (test) + 2 (jne) = 10 - 5 (5 byte jump 0) = 5 addition bytes.”…””}”(hhhjU  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h Mhj  hžhubh¾)”}”(hXØ  If we then include the padding bytes, the jump label code saves, 16 total bytes
of instruction memory for this small function. In this case the non-jump label
function is 80 bytes long. Thus, we have saved 20% of the instruction
footprint. We can in fact improve this even further, since the 5-byte no-op
really can be a 2-byte no-op since we can reach the branch with a 2-byte jmp.
However, we have not yet implemented optimal no-op sizes (they are currently
hard-coded).”h]”hXØ  If we then include the padding bytes, the jump label code saves, 16 total bytes
of instruction memory for this small function. In this case the non-jump label
function is 80 bytes long. Thus, we have saved 20% of the instruction
footprint. We can in fact improve this even further, since the 5-byte no-op
really can be a 2-byte no-op since we can reach the branch with a 2-byte jmp.
However, we have not yet implemented optimal no-op sizes (they are currently
hard-coded).”…””}”(hje  hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Mhj  hžhubh¾)”}”(hŒÇSince there are a number of static key API uses in the scheduler paths,
'pipe-test' (also known as 'perf bench sched pipe') can be used to show the
performance improvement. Testing done on 3.3.0-rc2:”h]”hŒÏSince there are a number of static key API uses in the scheduler paths,
â€˜pipe-testâ€™ (also known as â€˜perf bench sched pipeâ€™) can be used to show the
performance improvement. Testing done on 3.3.0-rc2:”…””}”(hjs  hjq  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h Mhj  hžhubh¾)”}”(hŒjump label disabled::”h]”hŒjump label disabled:”…””}”(hŒjump label disabled:”hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h M#hj  hžhubhÝ)”}”(hXä  Performance counter stats for 'bash -c /tmp/pipe-test' (50 runs):

       855.700314 task-clock                #    0.534 CPUs utilized            ( +-  0.11% )
          200,003 context-switches          #    0.234 M/sec                    ( +-  0.00% )
                0 CPU-migrations            #    0.000 M/sec                    ( +- 39.58% )
              487 page-faults               #    0.001 M/sec                    ( +-  0.02% )
    1,474,374,262 cycles                    #    1.723 GHz                      ( +-  0.17% )
  <not supported> stalled-cycles-frontend
  <not supported> stalled-cycles-backend
    1,178,049,567 instructions              #    0.80  insns per cycle          ( +-  0.06% )
      208,368,926 branches                  #  243.507 M/sec                    ( +-  0.06% )
        5,569,188 branch-misses             #    2.67% of all branches          ( +-  0.54% )

      1.601607384 seconds time elapsed                                          ( +-  0.07% )”h]”hXä  Performance counter stats for 'bash -c /tmp/pipe-test' (50 runs):

       855.700314 task-clock                #    0.534 CPUs utilized            ( +-  0.11% )
          200,003 context-switches          #    0.234 M/sec                    ( +-  0.00% )
                0 CPU-migrations            #    0.000 M/sec                    ( +- 39.58% )
              487 page-faults               #    0.001 M/sec                    ( +-  0.02% )
    1,474,374,262 cycles                    #    1.723 GHz                      ( +-  0.17% )
  <not supported> stalled-cycles-frontend
  <not supported> stalled-cycles-backend
    1,178,049,567 instructions              #    0.80  insns per cycle          ( +-  0.06% )
      208,368,926 branches                  #  243.507 M/sec                    ( +-  0.06% )
        5,569,188 branch-misses             #    2.67% of all branches          ( +-  0.54% )

      1.601607384 seconds time elapsed                                          ( +-  0.07% )”…””}”(hhhjŽ  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h M%hj  hžhubh¾)”}”(hŒjump label enabled::”h]”hŒjump label enabled:”…””}”(hŒjump label enabled:”hjœ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h M4hj  hžhubhÝ)”}”(hX­  Performance counter stats for 'bash -c /tmp/pipe-test' (50 runs):

       841.043185 task-clock                #    0.533 CPUs utilized            ( +-  0.12% )
          200,004 context-switches          #    0.238 M/sec                    ( +-  0.00% )
                0 CPU-migrations            #    0.000 M/sec                    ( +- 40.87% )
              487 page-faults               #    0.001 M/sec                    ( +-  0.05% )
    1,432,559,428 cycles                    #    1.703 GHz                      ( +-  0.18% )
  <not supported> stalled-cycles-frontend
  <not supported> stalled-cycles-backend
    1,175,363,994 instructions              #    0.82  insns per cycle          ( +-  0.04% )
      206,859,359 branches                  #  245.956 M/sec                    ( +-  0.04% )
        4,884,119 branch-misses             #    2.36% of all branches          ( +-  0.85% )

      1.579384366 seconds time elapsed”h]”hX­  Performance counter stats for 'bash -c /tmp/pipe-test' (50 runs):

       841.043185 task-clock                #    0.533 CPUs utilized            ( +-  0.12% )
          200,004 context-switches          #    0.238 M/sec                    ( +-  0.00% )
                0 CPU-migrations            #    0.000 M/sec                    ( +- 40.87% )
              487 page-faults               #    0.001 M/sec                    ( +-  0.05% )
    1,432,559,428 cycles                    #    1.703 GHz                      ( +-  0.18% )
  <not supported> stalled-cycles-frontend
  <not supported> stalled-cycles-backend
    1,175,363,994 instructions              #    0.82  insns per cycle          ( +-  0.04% )
      206,859,359 branches                  #  245.956 M/sec                    ( +-  0.04% )
        4,884,119 branch-misses             #    2.36% of all branches          ( +-  0.85% )

      1.579384366 seconds time elapsed”…””}”(hhhj«  ubah}”(h]”h ]”h"]”h$]”h&]”hìhíuh1hÜhŸh¶h M6hj  hžhubh¾)”}”(hX$  The percentage of saved branches is .7%, and we've saved 12% on
'branch-misses'. This is where we would expect to get the most savings, since
this optimization is about reducing the number of branches. In addition, we've
saved .2% on instructions, and 2.8% on cycles and 1.4% on elapsed time.”h]”hX,  The percentage of saved branches is .7%, and weâ€™ve saved 12% on
â€˜branch-missesâ€™. This is where we would expect to get the most savings, since
this optimization is about reducing the number of branches. In addition, weâ€™ve
saved .2% on instructions, and 2.8% on cycles and 1.4% on elapsed time.”…””}”(hj»  hj¹  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hŸh¶h MEhj  hžhubeh}”(h]”Œ'static-key-label-api-usage-and-examples”ah ]”h"]”Œ(static key label api, usage and examples”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kaubeh}”(h]”Œstatic-keys”ah ]”h"]”Œstatic keys”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jú  Œerror_encoding”ŒUTF-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h¶Œ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œembed_images”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(jÔ  jÑ  jR  jO  jy  jv  j  jþ  jÌ  jÉ  uŒ	nametypes”}”(jÔ  NjR  Njy  Nj  NjÌ  Nuh}”(jÑ  h£jO  j  jv  jU  jþ  j|  jÉ  j  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”(hŒsystem_message”“”)”}”(hhh]”h¾)”}”(hŒ:Enumerated list start value not ordinal-1: "4" (ordinal 4)”h]”hŒ>Enumerated list start value not ordinal-1: â€œ4â€ (ordinal 4)”…””}”(hhhjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hj_  ubah}”(h]”h ]”h"]”h$]”h&]”Œlevel”KŒtype”ŒINFO”Œsource”h¶Œline”Kuh1j]  hj  hžhhŸh¶h K´ubj^  )”}”(hhh]”h¾)”}”(hŒ:Enumerated list start value not ordinal-1: "5" (ordinal 5)”h]”hŒ>Enumerated list start value not ordinal-1: â€œ5â€ (ordinal 5)”…””}”(hhhj~  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h½hj{  ubah}”(h]”h ]”h"]”h$]”h&]”Œlevel”KŒtype”jx  Œsource”h¶Œline”Kuh1j]  hj  hžhhŸh¶h KÐubeŒtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
decoration”Nhžhub.