linux-kernel - Re: [PATCH] sched: Provide iowait counters

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Message-ID: <4A6A8AFE.1010608@linux.intel.com>
Date:	Fri, 24 Jul 2009 21:33:02 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	"Kok, Auke-jan H" <auke-jan.h.kok@...el.com>
Subject: Re: [PATCH] sched: Provide iowait counters

Andrew Morton wrote:
> On Mon, 20 Jul 2009 11:31:47 -0700 Arjan van de Ven <arjan@...ux.intel.com> wrote:
> 
>> For counting how long an application has been waiting for (disk) IO,
>> there currently is only the HZ sample driven information available, while
>> for all other counters in this class, a high resolution version is
>> available via CONFIG_SCHEDSTATS.
>>
>> In order to make an improved bootchart tool possible, we also need
>> a higher resolution version of the iowait time.
>>
>> This patch below adds this scheduler statistic to the kernel.
> 
> Doesn't this duplicate the delay accounting already available via the
> taskstats interface?

we have how long we wait. we do not have how long we iowait afaik...
at least not in nanosecond granularity. (We do have the sampled data, but that
is milisecond sampled data, not very useful for making charts based on time
to show the sequence of events)
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