linux-kernel - [RFC PATCH 0/2] sched: Improve cache locality of RSEQ concurrency IDs

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Message-Id: <20240903190650.53644-1-mathieu.desnoyers@efficios.com>
Date: Tue,  3 Sep 2024 15:06:48 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>,
	Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [RFC PATCH 0/2] sched: Improve cache locality of RSEQ concurrency IDs

Intermittent workloads behaving in bursts spaced by more than 100ms
on each CPU exhibit bad cache locality and degraded performance compared
to purely per-cpu data indexing, because concurrency IDs are allocated
over various CPUs and cores, therefore losing cache locality of the
associated data.

This series addresses this shortcoming. I observed speedups up to 16.7x
compared to plain mm_cid indexing in benchmarks.

It applies on top of v6.10.6.

This deprecates the prior "sched: NUMA-aware per-memory-map concurrency
IDs" patch series with a simpler and more general approach.

Feedback is welcome!

Thanks,

Mathieu

Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Yury Norov <yury.norov@...il.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>

Mathieu Desnoyers (2):
  cpumask: Implement cpumask_next_andnot
  sched: Improve cache locality of RSEQ concurrency IDs for intermittent
    workloads

 fs/exec.c                |  2 +-
 include/linux/cpumask.h  | 17 +++++++++++
 include/linux/mm_types.h | 66 ++++++++++++++++++++++++++++++++++------
 kernel/fork.c            |  2 +-
 kernel/sched/core.c      |  7 +++--
 kernel/sched/sched.h     | 47 +++++++++++++++++++---------
 6 files changed, 114 insertions(+), 27 deletions(-)

-- 
2.39.2