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| author | Tony Luck <tony.luck@intel.com> | 2023-12-04 10:53:57 -0800 |
|---|---|---|
| committer | Tony Luck <tony.luck@intel.com> | 2024-01-30 13:50:51 -0800 |
| commit | 0b486751af548487cb322a10d07cd181ab85b91b (patch) | |
| tree | 5dedca18c5f9e258350fb2b0ae04de13267ac638 | |
| parent | 70cc261bf5b20fc23e95dc15229b3ebf4226eb87 (diff) | |
| download | linux-snc_alt.tar.gz | |
x86/resctrl: Update documentation with Sub-NUMA cluster changessnc_alt
With Sub-NUMA Cluster mode enabled the scope of monitoring resources is
per-NODE instead of per-L3 cache. Suffixes of directories with "L3" in
their name refer to Sub-NUMA nodes instead of L3 cache ids.
Users should be aware that SNC mode also affects the amount of L3 cache
available for allocation within each SNC node.
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Peter Newman <peternewman@google.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Babu Moger <babu.moger@gmail.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
| -rw-r--r-- | Documentation/arch/x86/resctrl.rst | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst index a6279df64a9db8..15f1cff6ee7643 100644 --- a/Documentation/arch/x86/resctrl.rst +++ b/Documentation/arch/x86/resctrl.rst @@ -366,10 +366,10 @@ When control is enabled all CTRL_MON groups will also contain: When monitoring is enabled all MON groups will also contain: "mon_data": - This contains a set of files organized by L3 domain and by - RDT event. E.g. on a system with two L3 domains there will - be subdirectories "mon_L3_00" and "mon_L3_01". Each of these - directories have one file per event (e.g. "llc_occupancy", + This contains a set of files organized by L3 domain or by NUMA + node (depending on whether Sub-NUMA Cluster (SNC) mode is disabled + or enabled respectively) and by RDT event. Each of these + directories has one file per event (e.g. "llc_occupancy", "mbm_total_bytes", and "mbm_local_bytes"). In a MON group these files provide a read out of the current value of the event for all tasks in the group. In CTRL_MON groups these files provide @@ -478,6 +478,23 @@ if non-contiguous 1s value is supported. On a system with a 20-bit mask each bit represents 5% of the capacity of the cache. You could partition the cache into four equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000. +Notes on Sub-NUMA Cluster mode +============================== +When SNC mode is enabled, Linux may load balance tasks between Sub-NUMA +nodes much more readily than between regular NUMA nodes since the CPUs +on Sub-NUMA nodes share the same L3 cache and the system may report +the NUMA distance between Sub-NUMA nodes with a lower value than used +for regular NUMA nodes. Users who do not bind tasks to the CPUs of a +specific Sub-NUMA node must read the "llc_occupancy", "mbm_total_bytes", +and "mbm_local_bytes" for all Sub-NUMA nodes where the tasks may execute +to get the full view of traffic for which the tasks were the source. + +The cache allocation feature still provides the same number of +bits in a mask to control allocation into the L3 cache, but each +of those ways has its capacity reduced because the cache is divided +between the SNC nodes. The values reported in the resctrl +"size" files are adjusted accordingly. + Memory bandwidth Allocation and monitoring ========================================== |