€•!3      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)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ(/translations/zh_CN/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ(/translations/zh_TW/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ(/translations/it_IT/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ(/translations/ja_JP/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ(/translations/ko_KR/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ(/translations/sp_SP/admin-guide/cpu-load”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒCPU load”h]”hŒCPU load”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒB/var/lib/git/docbuild/linux/Documentation/admin-guide/cpu-load.rst”h KubhŒ	paragraph”“”)”}”(hŒÊLinux exports various bits of information via ``/proc/stat`` and
``/proc/uptime`` that userland tools, such as top(1), use to calculate
the average time system spent in a particular state, for example::”h]”(hŒ.Linux exports various bits of information via ”…””}”(hh¹hžhhŸNh NubhŒliteral”“”)”}”(hŒ``/proc/stat``”h]”hŒ
/proc/stat”…””}”(hhÃhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhh¹ubhŒ and
”…””}”(hh¹hžhhŸNh NubhÂ)”}”(hŒ``/proc/uptime``”h]”hŒ/proc/uptime”…””}”(hhÕhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhh¹ubhŒx that userland tools, such as top(1), use to calculate
the average time system spent in a particular state, for example:”…””}”(hh¹hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhŒliteral_block”“”)”}”(hŒ©$ iostat
Linux 2.6.18.3-exp (linmac)     02/20/2007

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          10.01    0.00    2.92    5.44    0.00   81.63

...”h]”hŒ©$ iostat
Linux 2.6.18.3-exp (linmac)     02/20/2007

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          10.01    0.00    2.92    5.44    0.00   81.63

...”…””}”hhïsbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1híhŸh¶h K	hh£hžhubh¸)”}”(hŒ¸Here the system thinks that over the default sampling period the
system spent 10.01% of the time doing work in user space, 2.92% in the
kernel, and was overall 81.63% of the time idle.”h]”hŒ¸Here the system thinks that over the default sampling period the
system spent 10.01% of the time doing work in user space, 2.92% in the
kernel, and was overall 81.63% of the time idle.”…””}”(hhÿhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒÄIn most cases the ``/proc/stat``         information reflects the reality quite
closely, however due to the nature of how/when the kernel collects
this data sometimes it can not be trusted at all.”h]”(hŒIn most cases the ”…””}”(hj  hžhhŸNh NubhÂ)”}”(hŒ``/proc/stat``”h]”hŒ
/proc/stat”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj  ubhŒ¤         information reflects the reality quite
closely, however due to the nature of how/when the kernel collects
this data sometimes it can not be trusted at all.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hX‰  So how is this information collected?  Whenever timer interrupt is
signalled the kernel looks what kind of task was running at this
moment and increments the counter that corresponds to this tasks
kind/state.  The problem with this is that the system could have
switched between various states multiple times between two timer
interrupts yet the counter is incremented only for the last state.”h]”hX‰  So how is this information collected?  Whenever timer interrupt is
signalled the kernel looks what kind of task was running at this
moment and increments the counter that corresponds to this tasks
kind/state.  The problem with this is that the system could have
switched between various states multiple times between two timer
interrupts yet the counter is incremented only for the last state.”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¢)”}”(hhh]”(h§)”}”(hŒExample”h]”hŒExample”…””}”(hj>  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj;  hžhhŸh¶h K"ubh¸)”}”(hŒ_If we imagine the system with one task that periodically burns cycles
in the following manner::”h]”hŒ^If we imagine the system with one task that periodically burns cycles
in the following manner:”…””}”(hjL  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K$hj;  hžhubhî)”}”(hX%   time line between two timer interrupts
|--------------------------------------|
 ^                                    ^
 |_ something begins working          |
                                      |_ something goes to sleep
                                     (only to be awaken quite soon)”h]”hX%   time line between two timer interrupts
|--------------------------------------|
 ^                                    ^
 |_ something begins working          |
                                      |_ something goes to sleep
                                     (only to be awaken quite soon)”…””}”hjZ  sbah}”(h]”h ]”h"]”h$]”h&]”hýhþuh1híhŸh¶h K'hj;  hžhubh¸)”}”(hŒÛIn the above situation the system will be 0% loaded according to the
``/proc/stat`` (since the timer interrupt will always happen when the
system is executing the idle handler), but in reality the load is
closer to 99%.”h]”(hŒEIn the above situation the system will be 0% loaded according to the
”…””}”(hjh  hžhhŸNh NubhÂ)”}”(hŒ``/proc/stat``”h]”hŒ
/proc/stat”…””}”(hjp  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjh  ubhŒˆ (since the timer interrupt will always happen when the
system is executing the idle handler), but in reality the load is
closer to 99%.”…””}”(hjh  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K.hj;  hžhubh¸)”}”(hŒ…One can imagine many more situations where this behavior of the kernel
will lead to quite erratic information inside ``/proc/stat``::”h]”(hŒuOne can imagine many more situations where this behavior of the kernel
will lead to quite erratic information inside ”…””}”(hjˆ  hžhhŸNh NubhÂ)”}”(hŒ``/proc/stat``”h]”hŒ
/proc/stat”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjˆ  ubhŒ:”…””}”(hjˆ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K3hj;  hžhubhî)”}”(hXW  /* gcc -o hog smallhog.c */
#include <time.h>
#include <limits.h>
#include <signal.h>
#include <sys/time.h>
#define HIST 10

static volatile sig_atomic_t stop;

static void sighandler(int signr)
{
        (void) signr;
        stop = 1;
}

static unsigned long hog (unsigned long niters)
{
        stop = 0;
        while (!stop && --niters);
        return niters;
}

int main (void)
{
        int i;
        struct itimerval it = {
                .it_interval = { .tv_sec = 0, .tv_usec = 1 },
                .it_value    = { .tv_sec = 0, .tv_usec = 1 } };
        sigset_t set;
        unsigned long v[HIST];
        double tmp = 0.0;
        unsigned long n;
        signal(SIGALRM, &sighandler);
        setitimer(ITIMER_REAL, &it, NULL);

        hog (ULONG_MAX);
        for (i = 0; i < HIST; ++i) v[i] = ULONG_MAX - hog(ULONG_MAX);
        for (i = 0; i < HIST; ++i) tmp += v[i];
        tmp /= HIST;
        n = tmp - (tmp / 3.0);

        sigemptyset(&set);
        sigaddset(&set, SIGALRM);

        for (;;) {
                hog(n);
                sigwait(&set, &i);
        }
        return 0;
}”h]”hXW  /* gcc -o hog smallhog.c */
#include <time.h>
#include <limits.h>
#include <signal.h>
#include <sys/time.h>
#define HIST 10

static volatile sig_atomic_t stop;

static void sighandler(int signr)
{
        (void) signr;
        stop = 1;
}

static unsigned long hog (unsigned long niters)
{
        stop = 0;
        while (!stop && --niters);
        return niters;
}

int main (void)
{
        int i;
        struct itimerval it = {
                .it_interval = { .tv_sec = 0, .tv_usec = 1 },
                .it_value    = { .tv_sec = 0, .tv_usec = 1 } };
        sigset_t set;
        unsigned long v[HIST];
        double tmp = 0.0;
        unsigned long n;
        signal(SIGALRM, &sighandler);
        setitimer(ITIMER_REAL, &it, NULL);

        hog (ULONG_MAX);
        for (i = 0; i < HIST; ++i) v[i] = ULONG_MAX - hog(ULONG_MAX);
        for (i = 0; i < HIST; ++i) tmp += v[i];
        tmp /= HIST;
        n = tmp - (tmp / 3.0);

        sigemptyset(&set);
        sigaddset(&set, SIGALRM);

        for (;;) {
                hog(n);
                sigwait(&set, &i);
        }
        return 0;
}”…””}”hj¨  sbah}”(h]”h ]”h"]”h$]”h&]”hýhþuh1híhŸh¶h K7hj;  hžhubeh}”(h]”Œexample”ah ]”h"]”Œexample”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K"ubh¢)”}”(hhh]”(h§)”}”(hŒ
References”h]”hŒ
References”…””}”(hjÁ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj¾  hžhhŸh¶h KlubhŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒAhttps://lore.kernel.org/r/loom.20070212T063225-663@post.gmane.org”h]”h¸)”}”(hjØ  h]”hŒ	reference”“”)”}”(hjØ  h]”hŒAhttps://lore.kernel.org/r/loom.20070212T063225-663@post.gmane.org”…””}”(hjß  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”jØ  uh1jÝ  hjÚ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KnhjÖ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jÔ  hjÑ  hžhhŸh¶h NubjÕ  )”}”(hŒ*Documentation/filesystems/proc.rst (1.8)

”h]”h¸)”}”(hŒ(Documentation/filesystems/proc.rst (1.8)”h]”hŒ(Documentation/filesystems/proc.rst (1.8)”…””}”(hjý  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kohjù  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jÔ  hjÑ  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1jÏ  hŸh¶h Knhj¾  hžhubeh}”(h]”Œ
references”ah ]”h"]”Œ
references”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Klubh¢)”}”(hhh]”(h§)”}”(hŒThanks”h]”hŒThanks”…””}”(hj$  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj!  hžhhŸh¶h Ksubh¸)”}”(hŒCon Kolivas, Pavel Machek”h]”hŒCon Kolivas, Pavel Machek”…””}”(hj2  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kuhj!  hžhubeh}”(h]”Œthanks”ah ]”h"]”Œthanks”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Ksubeh}”(h]”Œcpu-load”ah ]”h"]”Œcpu load”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”js  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file_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œ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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”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(jM  jJ  j»  j¸  j  j  jE  jB  uŒ	nametypes”}”(jM  ‰j»  ‰j  ‰jE  ‰uh}”(jJ  h£j¸  j;  j  j¾  jB  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”]”Œtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
decoration”Nhžhub.