linux-kernel - Re: [PATCH v3] vmpressure: wake up work only when there is registration event

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Message-ID: <YU3ciRm7L2p9lJo6@dhcp22.suse.cz>
Date:   Fri, 24 Sep 2021 16:11:21 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     yongw.pur@...il.com
Cc:     tj@...nel.org, peterz@...radead.org, wang.yong12@....com.cn,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, yang.yang29@....com.cn
Subject: Re: [PATCH v3] vmpressure: wake up work only when there is
 registration event

On Fri 24-09-21 06:44:25, yongw.pur@...il.com wrote:
> From: wangyong <wang.yong12@....com.cn>
> 
> Use the global variable num_events to record the number of vmpressure
> events registered by the system, and wake up work only when there
> is registration event.
> Usually, the vmpressure event is not registered in the system, this patch
> can avoid waking up work and doing nothing.
> 
> Test with 5.14.0-rc5-next-20210813 on x86_64 4G ram.
> Consume cgroup memory until it is about to be reclaimed, then execute
> "perf stat -I 2000 malloc.out" command to trigger memory reclamation
> and get performance results.
> The context-switches is reduced by about 20 times.
> 
> unpatched:
> Average of 10 test results
> 582.4674048     task-clock(msec)
> 19910.8         context-switches
> 0               cpu-migrations
> 1292.9          page-faults
> 414784733.1     cycles
> 580070698.4     instructions
> 125572244.7     branches
> 2073541.2       branch-misses
> 
> patched:
> Average of 10 test results
> 973.6174796     task-clock(msec)
> 988.6           context-switches
> 0               cpu-migrations
> 1785.2          page-faults
> 772883602.4     cycles
> 1360280911      instructions
> 290519434.9     branches
> 3378378.2       branch-misses

Your data still doesn't make any sense. I have asked about that in the
previous submission and you haven't really clarified anything. How come
your task-clock has almost doubled. You are likely not not comparing
apples to apples or something weird is going on.

This patch is not going to fly without a sensible data and analysis of
that data.

Thanks!
-- 
Michal Hocko
SUSE Labs