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Message-ID: <4A6A8E96.7050509@linux.intel.com>
Date: Fri, 24 Jul 2009 21:48:22 -0700
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
       "Kok, Auke-jan H" <auke-jan.h.kok@intel.com>
Subject: Re: [PATCH] sched: Provide iowait counters
References: <4A64B813.1080506@linux.intel.com>	<20090724212220.afa278ee.akpm@linux-foundation.org>	<4A6A8AFE.1010608@linux.intel.com> <20090724214006.7380c3b4.akpm@linux-foundation.org>
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Andrew Morton wrote:
> On Fri, 24 Jul 2009 21:33:02 -0700 Arjan van de Ven <arjan@linux.intel.com> wrote:
> 
>> Andrew Morton wrote:
>>> On Mon, 20 Jul 2009 11:31:47 -0700 Arjan van de Ven <arjan@linux.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)
> 
> See include/linux/sched.h's definition of task_delay_info - u64
> blkio_delay is in nanoseconds.  It uses
> do_posix_clock_monotonic_gettime() internally.

looks like it does.. to bad we don't expose that data in a /proc/<pid>/delay or something field
like we do with the scheduler info...


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