linux-kernel - [PATCH V5 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

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Message-ID: <20250530181103.34563-1-qinyuntan@linux.alibaba.com>
Date: Sat, 31 May 2025 02:11:02 +0800
From: Qinyun Tan <qinyuntan@...ux.alibaba.com>
To: Tony Luck <tony.luck@...el.com>
Cc: "H . Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Reinette Chatre <reinette.chatre@...el.com>,
	Qinyun Tan <qinyuntan@...ux.alibaba.com>
Subject: [PATCH V5 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

V5:
- Modify the commit log format again. I am truly grateful to Reinette
  for her thoughtful guidance :).

V4:
- Add the tested by and reviewed by tags.
- Modify the commit log format.

V3:
- According to Reinette suggestion, modify the commit log description to
 make it easier for readers to understand

V2:
- Keep sanity checks in the __mon_event_count to ensure execution occurs
  exclusively on CPUs sharing the same L3 cache cluster
- When reading the top level event, obtain a CPU within hdr.cpu_mask.
  Then use the cacheinfo shared_cpu_map of this CPU instead of using
  hdr.cpu_mask directly
- Adjust code formatting and commit log descriptions.

In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
structure representing a NUMA node relies on the cacheinfo interface
(rdt_mon_domain::ci) to store L3 cache information (e.g., shared_cpu_map)
for monitoring. The L3 cache information of a SNC NUMA node determines
which domains are summed for the "top level" L3-scoped events.

rdt_mon_domain::ci is initialized using the first online CPU of a NUMA
node. When this CPU goes offline, its shared_cpu_map is cleared to contain
only the offline CPU itself. Subsequently, attempting to read counters
via smp_call_on_cpu(offline_cpu) fails (and error ignored), returning
zero values for "top-level events" without any error indication.

Replace the cacheinfo references in struct rdt_mon_domain and struct
rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).

rdt_domain_hdr::cpu_mask contains the online CPUs associated with that
domain. When reading "top-level events", select a CPU from
rdt_domain_hdr::cpu_mask and utilize its L3 shared_cpu_map to determine
valid CPUs for reading RMID counter via the MSR interface.

Considering all CPUs associated with the L3 cache improves the chances
of picking a housekeeping CPU on which the counter reading work can be
queued, avoiding an unnecessary IPI.

Qinyun Tan (1):
  x86/resctrl: Remove unappropriate references to cacheinfo in the
    resctrl subsystem.

 arch/x86/kernel/cpu/resctrl/core.c |  6 ++++--
 fs/resctrl/ctrlmondata.c           | 13 +++++++++----
 fs/resctrl/internal.h              |  4 ++--
 fs/resctrl/monitor.c               |  6 ++++--
 fs/resctrl/rdtgroup.c              |  6 +++---
 include/linux/resctrl.h            |  4 ++--
 6 files changed, 24 insertions(+), 15 deletions(-)

-- 
2.43.5