linux-kernel - Re: [PATCH 1/2 v2.0]sched: Removing unused fields from /proc/schedstat

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Date:	Thu, 03 Feb 2011 18:19:26 +0900
From:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>
To:	Ciju Rajan K <ciju@...ux.vnet.ibm.com>
CC:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>
Subject: Re: [PATCH 1/2 v2.0]sched: Removing unused fields from /proc/schedstat

Hi Ciju,

(2011/02/02 17:54), Ciju Rajan K wrote:
> Hi Satoru,
>
>
>>> I think we can remove rq->sched_switch and rq->sched_switch
>>> without no problem because they are meaningless. The former
>>> is for old O(1) scheduler and means the number of runqueue
>>> switching among active/expired queue. The latter is for
>>> SD_WAKE_BALANCE flag and its logic is already gone.
>>>
>>> However sbe_* are for SD_BALANCE_EXEC flag and sbf_* are for
>>> SD_BALANCE_FORK flag. Since both logic for them are still alive,
>>> the absence of these accounting is regression in my perspective.
>>> In addition, these fields would be useful for analyzing load
>>> balance behavior.
>>>
>
> The sbe_*&  sbf_* counters were added by the commit
> 68767a0ae428801649d510d9a65bb71feed44dd1 But it was subsequently
> removed by the commit 476d139c218e44e045e4bc6d4cc02b010b343939

OK, I understood. It's OK if user tools referring /proc/schedstat
are released sync with this change.

I confirmed the following:

  - This patch removes some unused schedstat fields and related
    data.
  - The kernel applying this patch works fine on my i386 box.

Tested-by: Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>

Thanks,
Satoru

>
> [ciju@...u kernel]$ git describe 68767a0ae428801649d510d9a65bb71feed44dd1 --contains
> v2.6.13-rc1~68^2~148
> [ciju@...u kernel]$ git describe 476d139c218e44e045e4bc6d4cc02b010b343939 --contains
> v2.6.13-rc1~68^2~140
>
> So.. it was introduced and removed in 2.6.13 time frame
>
>
> When the counters were removed the sbe_* sbf_* variable
> declarations were not removed. Hence it caused a little confusion.
> So I believe these stats were not available and hence can't be
> considered as regression.
>
> 476d139c218e44e045e4bc6d4cc02b010b343939 consolidated the fork and
> exec balance. Thereafter it became non-trivial to provide separate
> stats for fork and exec events. So if people think a consolidated
> balance-on-event is needed, it can be looked into separately. But
> that shouldn't prevent this documentation cleanup patch from
> getting in.
>
> -Ciju
>
>
> --
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