linux-kernel - Re: [PATCH v18 17/17] x86/resctrl: Update documentation with Sub-NUMA cluster changes

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Date: Thu, 16 May 2024 10:57:21 +0200
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Tony Luck <tony.luck@...el.com>
CC: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre
	<reinette.chatre@...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>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v18 17/17] x86/resctrl: Update documentation with
 Sub-NUMA cluster changes

On 2024-05-15 at 15:23:25 -0700, Tony Luck wrote:
>*** This patch needs updating for new files for monitoring ***

Is this note here by accident? New files seem to be mentioned in the patch.

>
>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.
>
>Signed-off-by: Tony Luck <tony.luck@...el.com>
>---
> Documentation/arch/x86/resctrl.rst | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
>diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>index 627e23869bca..401f6bfb4a3c 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 (SNC) cluster 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 +488,19 @@ 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 and monitoring
> ==========================================
> 
>-- 
>2.44.0
>

-- 
Kind regards
Maciej Wieczór-Retman