x86/resctrl: Update documentation with Sub-NUMA cluster changes
With Sub-NUMA Cluster (SNC) mode enabled, the scope of monitoring resources is per-NODE instead of per-L3 cache. Backwards compatibility is maintained by providing files in the mon_L3_XX directories that sum event counts for all SNC nodes sharing an L3 cache. New files provide per-SNC node event counts. Users should be aware that SNC mode also affects the amount of L3 cache available for allocation within each SNC node. Signed-off-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com> Tested-by: Babu Moger <babu.moger@amd.com> Link: https://lore.kernel.org/r/20240628215619.76401-20-tony.luck@intel.com
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@ -375,6 +375,10 @@ When monitoring is enabled all MON groups will also contain:
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all tasks in the group. In CTRL_MON groups these files provide
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all tasks in the group. In CTRL_MON groups these files provide
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the sum for all tasks in the CTRL_MON group and all tasks in
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the sum for all tasks in the CTRL_MON group and all tasks in
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MON groups. Please see example section for more details on usage.
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MON groups. Please see example section for more details on usage.
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On systems with Sub-NUMA Cluster (SNC) enabled there are extra
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directories for each node (located within the "mon_L3_XX" directory
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for the L3 cache they occupy). These are named "mon_sub_L3_YY"
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where "YY" is the node number.
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"mon_hw_id":
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"mon_hw_id":
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Available only with debug option. The identifier used by hardware
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Available only with debug option. The identifier used by hardware
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@ -484,6 +488,29 @@ if non-contiguous 1s value is supported. On a system with a 20-bit mask
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each bit represents 5% of the capacity of the cache. You could partition
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each bit represents 5% of the capacity of the cache. You could partition
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the cache into four equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000.
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the cache into four equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000.
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Notes on Sub-NUMA Cluster mode
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==============================
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When SNC mode is enabled, Linux may load balance tasks between Sub-NUMA
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nodes much more readily than between regular NUMA nodes since the CPUs
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on Sub-NUMA nodes share the same L3 cache and the system may report
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the NUMA distance between Sub-NUMA nodes with a lower value than used
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for regular NUMA nodes.
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The top-level monitoring files in each "mon_L3_XX" directory provide
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the sum of data across all SNC nodes sharing an L3 cache instance.
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Users who bind tasks to the CPUs of a specific Sub-NUMA node can read
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the "llc_occupancy", "mbm_total_bytes", and "mbm_local_bytes" in the
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"mon_sub_L3_YY" directories to get node local data.
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Memory bandwidth allocation is still performed at the L3 cache
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level. I.e. throttling controls are applied to all SNC nodes.
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L3 cache allocation bitmaps also apply to all SNC nodes. But note that
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the amount of L3 cache represented by each bit is divided by the number
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of SNC nodes per L3 cache. E.g. with a 100MB cache on a system with 10-bit
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allocation masks each bit normally represents 10MB. With SNC mode enabled
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with two SNC nodes per L3 cache, each bit only represents 5MB.
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Memory bandwidth Allocation and monitoring
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Memory bandwidth Allocation and monitoring
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==========================================
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==========================================
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