On 12/4/2023 12:53 PM, Tony Luck wrote:
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@xxxxxxxxx>
Tested-by: Shaopeng Tan<tan.shaopeng@xxxxxxxxxxxxxx>
Reviewed-by: Peter Newman<peternewman@xxxxxxxxxx>
Reviewed-by: Reinette Chatre<reinette.chatre@xxxxxxxxx>
Reviewed-by: Shaopeng Tan<tan.shaopeng@xxxxxxxxxxxxxx>
Reviewed-by: Babu Moger <babu.moger@xxxxxxxxx>
---
Documentation/arch/x86/resctrl.rst | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index a6279df64a9d..15f1cff6ee76 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
==========================================
