linux-kernel - Re: [RFC][PATCH 0/2 v1.0]sched: updating /proc/schedstat

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Date:	Tue, 18 Jan 2011 13:20:03 +0530
From:	Ciju Rajan K <ciju@...ux.vnet.ibm.com>
To:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 0/2 v1.0]sched: updating /proc/schedstat



On 01/18/2011 12:59 PM, Satoru Takeuchi wrote:
> Hi Ciju,
> 
Hello Satoru,

> I don't like this patches because it breaks backward compatibility.
> If there are any user who uses these fields, they can't get
> the information which these fields provides from this time on.
> In this context, `user' means not only application but also the person
> who refers to /proc/schedstat directly.

This patch set removes only those fields which are currently not in use.
If you observe the fields of /proc/schedstat the following fields are not
being updated.

For each cpu:

2) sched_switch

For each domain:

28) sd->sbe_count
29) sd->sbe_balanced
30) sd->sbe_pushed
31) sd->sbf_count
32) sd->sbf_balanced 
33) sd->sbf_pushed
36) sd->ttwu_move_balance

The serial numbers indicate the positions of the fields in version 15 
of/proc/schedstat
> 
> In fact, although I can't say "command XXX refers to these field",
> I sometimes check {sbe_*,sbf_*} to confirm load_balance behavior
> by issuing, for example,
> 
> ===============================================================================
> watch /proc/schedstat
> ===============================================================================
> 
> or
> 
> ===============================================================================
> while true ; do
> cat /proc/schedstat >>schedstat_log
> sleep 10
> done
> ===============================================================================

Only concern is that the user might have to update the scripts to get the
correct position of the fields. Which anyway the scripts have to take care
depending on the version of /proc/schedstat.

I hope this addresses your concern.

-Ciju
> 
> Thanks
> Satoru
> 
>>
>>
>>>
>>> Also, attachment fail.
>>
>> It should be ok now.
>>
>> -Ciju
>> -- 
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> 
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