linux-kernel - Re: [PATCH: 2.6.18.1] delayacct: cpu_count in taskstats updated correctly

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Date:	Fri, 27 Oct 2006 11:49:40 -0400
From:	Shailabh Nagar <nagar@...son.ibm.com>
To:	David Rientjes <rientjes@...washington.edu>
CC:	Martin Tostrup Setek <martitse@...dent.matnat.uio.no>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH: 2.6.18.1] delayacct: cpu_count in taskstats updated correctly

David Rientjes wrote:
> On Fri, 27 Oct 2006, Martin Tostrup Setek wrote:
> 
>> from: Martin T. Setek <martitse@....uio.no>
>>
>> cpu_count in struct taskstats should be the same as the corresponding (third)
>> value found in /proc/<pid>/schedstat
> 
> I disagree in favor of Documentation/accounting/taskstats-struct.txt.
> cpu_count is the number of delay values recorded, so accumulating them is 
> appropriate.
> 
> 		David

David's right. The delay accounting field cpu_count
is measuring how many delay values are recorded in the field cpu_delay_total
(so that one can divide one by the other to get an average if needed).

For the delays reported for a single task (ie. __delayacct_add_tsk called only
once for a given task), the effect will be what Martin wants i.e. cpu_count will be
the same as /proc/pid/schedstat's third field (sched_info->pcnt)

But when the delays are reported for a tgid, where *accumalation* of delays for
all constituent pids is being done (by calling __delayacct_add_tsk repeatedly), what
is desired is to accumalate both cpu_count and cpu_delay_total.

So the patch proposed by Martin is incorrect.

--Shailabh
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