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Date: Fri, 21 Jun 2024 15:38:59 -0700 From: Tony Luck <tony.luck@...el.com> To: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre <reinette.chatre@...el.com>, Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin <Dave.Martin@....com> Cc: x86@...nel.org, linux-kernel@...r.kernel.org, patches@...ts.linux.dev, Tony Luck <tony.luck@...el.com> Subject: [PATCH v21 18/18] 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@...el.com> Reviewed-by: Reinette Chatre <reinette.chatre@...el.com> --- Documentation/arch/x86/resctrl.rst | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst index 627e23869bca..a824affd741d 100644 --- a/Documentation/arch/x86/resctrl.rst +++ b/Documentation/arch/x86/resctrl.rst @@ -375,6 +375,10 @@ When monitoring is enabled all MON groups will also contain: all tasks in the group. In CTRL_MON groups these files provide the sum for all tasks in the CTRL_MON group and all tasks in MON groups. Please see example section for more details on usage. + On systems with Sub-NUMA Cluster (SNC) enabled there are extra + directories for each node (located within the "mon_L3_XX" directory + for the L3 cache they occupy). These are named "mon_sub_L3_YY" + where "YY" is the node number. "mon_hw_id": Available only with debug option. The identifier used by hardware @@ -484,6 +488,29 @@ 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. + +The top-level monitoring files in each "mon_L3_XX" directory provide +the sum of data across all SNC nodes sharing an L3 cache instance. +Users who bind tasks to the CPUs of a specific Sub-NUMA node can read +the "llc_occupancy", "mbm_total_bytes", and "mbm_local_bytes" in the +"mon_sub_L3_YY" directories to get node local data. + +Memory bandwidth allocation is still performed at the L3 cache +level. I.e. throttling controls are applied to all SNC nodes. + +L3 cache allocation bitmaps also apply to all SNC nodes. But note that +the amount of L3 cache represented by each bit is divided by the number +of SNC nodes per L3 cache. E.g. with a 100MB cache on a system with 10-bit +allocation masks each bit normally represents 10MB. With SNC mode enabled +with two SNC nodes per L3 cache, each bit only represents 5MB. + Memory bandwidth Allocation and monitoring ========================================== -- 2.45.2
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