linux-kernel - Re: [PATCH] docs/scheduler: Change unit of cpu_time and rq

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Date:   Fri, 8 Apr 2022 13:45:35 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "brookxu.cn" <brookxu.cn@...il.com>
Cc:     corbet@....net, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH] docs/scheduler: Change unit of cpu_time and rq_time to
 nanoseconds

On Fri, Apr 08, 2022 at 05:31:06PM +0800, brookxu.cn wrote:
> From: Chunguang Xu <brookxu@...cent.com>
> 
> In the current implementation, cpu_time and rq_time should be
> in nanoseconds, so this document needs to be modified.

I agree that this is wrong, but we shouldn't be changing the units
of measurement reported to userspace without changing the schedstats
version.  I suspect this was an inadvertent change, and we should be
converting from sched_clock() time (~= ns) to jiffies in show_schedstat().
Adding scheduler experts.

> Signed-off-by: Chunguang Xu <brookxu@...cent.com>
> ---
>  Documentation/scheduler/sched-stats.rst | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/scheduler/sched-stats.rst b/Documentation/scheduler/sched-stats.rst
> index dd9b99a..9078a27 100644
> --- a/Documentation/scheduler/sched-stats.rst
> +++ b/Documentation/scheduler/sched-stats.rst
> @@ -56,9 +56,9 @@ Next two are try_to_wake_up() statistics:
>  
>  Next three are statistics describing scheduling latency:
>  
> -     7) sum of all time spent running by tasks on this processor (in jiffies)
> +     7) sum of all time spent running by tasks on this processor (in nanoseconds)
>       8) sum of all time spent waiting to run by tasks on this processor (in
> -        jiffies)
> +        nanoseconds)
>       9) # of timeslices run on this cpu
>  
>  
> -- 
> 1.8.3.1
>