linux-kernel - [tip: x86/cache] x86/resctrl: Update documentation with Sub-NUMA cluster changes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <171994825095.2215.6815730382821505563.tip-bot2@tip-bot2>
Date: Tue, 02 Jul 2024 19:24:10 -0000
From: "tip-bot2 for Tony Luck" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Tony Luck <tony.luck@...el.com>, "Borislav Petkov (AMD)" <bp@...en8.de>,
 Reinette Chatre <reinette.chatre@...el.com>, Babu Moger <babu.moger@....com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/cache] x86/resctrl: Update documentation with Sub-NUMA
 cluster changes

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     ea34999f41873c96ac89e861e5fdfc7d0403f9e3
Gitweb:        https://git.kernel.org/tip/ea34999f41873c96ac89e861e5fdfc7d0403f9e3
Author:        Tony Luck <tony.luck@...el.com>
AuthorDate:    Fri, 28 Jun 2024 14:56:19 -07:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Tue, 02 Jul 2024 20:03:19 +02:00

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>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Tested-by: Babu Moger <babu.moger@....com>
Link: https://lore.kernel.org/r/20240628215619.76401-20-tony.luck@intel.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 627e238..a824aff 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
 ==========================================