linux-kernel - [PATCH v4 0/3] cgroup/rstat: Reduce cpu_lock hold time in cgroup_rstat_flush

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Message-Id: <20231106210543.717486-1-longman@redhat.com>
Date:   Mon,  6 Nov 2023 16:05:40 -0500
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Joe Mario <jmario@...hat.com>,
        Sebastian Jug <sejug@...hat.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v4 0/3] cgroup/rstat: Reduce cpu_lock hold time in cgroup_rstat_flush_locked()

 v4:
  - Update patch 2 to fix a minor bug and update some of the comments.

 v3:
  - Minor comment twisting as suggested by Yosry.
  - Add patches 2 and 3 to further reduce lock hold time

The purpose of this patch series is to reduce of the cpu_lock hold time
in cgroup_rstat_flush_locked() so as to reduce the latency impact when
cgroup_rstat_updated() is called as they may contend with each other
on the cpu_lock.

A parallel kernel build on a 2-socket x86-64 server is used as the
benchmarking tool for measuring the lock hold time. Below were the lock
hold time frequency distribution before and after applying different
number of patches:

  Hold time   Before patch   Patch 1   Patches 1-2  Patches 1-3
  ---------   ------------   -------   -----------  -----------
    0-01 us      804,139   13,738,708   14,594,545   15,484,707
   01-05 us    9,772,767    1,177,194      439,926      207,382
   05-10 us    4,595,028        4,984        5,960        3,174
   10-15 us      303,481        3,562        3,543        3,006
   15-20 us       78,971        1,314        1,397        1,066
   20-25 us       24,583           18           25           15
   25-30 us        6,908           12           12           10
   30-40 us        8,015
   40-50 us        2,192
   50-60 us          316
   60-70 us           43
   70-80 us            7
   80-90 us            2
     >90 us            3

Waiman Long (3):
  cgroup/rstat: Reduce cpu_lock hold time in cgroup_rstat_flush_locked()
  cgroup/rstat: Optimize cgroup_rstat_updated_list()
  cgroup: Avoid false cacheline sharing of read mostly rstat_cpu

 include/linux/cgroup-defs.h |  14 ++++
 kernel/cgroup/rstat.c       | 131 +++++++++++++++++++++---------------
 2 files changed, 91 insertions(+), 54 deletions(-)

-- 
2.39.3