linux-kernel - Re: [PATCH] sched: Update scheduler stat documentation.

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Message-ID: <20120116083615.GB23622@elte.hu>
Date:	Mon, 16 Jan 2012 09:36:15 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Update scheduler stat documentation.


* Rakib Mullick <rakib.mullick@...il.com> wrote:

> On Mon, Jan 16, 2012 at 1:56 PM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > * Rakib Mullick <rakib.mullick@...il.com> wrote:
> >
> >> /proc/schedstat's second field reflect to # of time context switch happened not # of times switched to the expired queue.
> >>
> >> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
> >> ---
> >>
> >> diff --git a/Documentation/scheduler/sched-stats.txt b/Documentation/scheduler/sched-stats.txt
> >> index 1cd5d51..7d8e12c 100644
> >> --- a/Documentation/scheduler/sched-stats.txt
> >> +++ b/Documentation/scheduler/sched-stats.txt
> >> @@ -38,7 +38,8 @@ First field is a sched_yield() statistic:
> >>       1) # of times sched_yield() was called
> >>
> >>  Next three are schedule() statistics:
> >> -     2) # of times we switched to the expired queue and reused it
> >> +     2) # of times context switch happened. This field is not utilized these
> >> +     days but kept for holding userspace tools integrity.
> >
> > if it's not used by anything but kept for the ABI then we should
> > not put context switch number in there, but always keep it zero,
> > right?
> >
>
> Yes, quite right. It is a bit confusing. Anyone might have 
> think that context switch numbers are 0. So, instead of saying 
> "# of times context switch happened", we can say, "This field 
> has been kept for ABI integrity". Right?

Yes - but we should also change it to export a value of zero. 
The field is a legacy 'array expirations' field, and as such it 
should be zero.

Thanks,

	Ingo
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