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From: Divyesh Shah <dpshah@google.com>
Date: Sat, 12 Jun 2010 08:51:54 -0700
Message-ID: <AANLkTinXZ3lHxTcusKxcPG-FWvykcfiDB9lcpZIPLEKx@mail.gmail.com>
Subject: Re: [PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio 
	cgroup stats.
To: Ingo Molnar <mingo@elte.hu>
Cc: jaxboe@fusionio.com, peterz@infradead.org, piotr@hosowicz.com,
       linux-kernel@vger.kernel.org, vgoyal@redhat.com,
       Thomas Gleixner <tglx@linutronix.de>
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On Sat, Jun 12, 2010 at 12:18 AM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Divyesh Shah <dpshah@google.com> wrote:
>
>> This will take care of the pre-emptive kernel issue and the unbounded
>> TSC drift problem. We will lose resolution though in some cases.
>
>> - ? ? blkg->stats.start_group_wait_time = sched_clock();
>> + ? ? blkg->stats.start_group_wait_time = ktime_to_ns(ktime_get());
>
> Ugh!
>
> ktime_get() can have insanely high overhead. Peter has added local_clock(), if
> then you should use that and apply checks to make sure the result isnt
> negative.

Ok. The negative checks are already in the code.

>
> ? ? ? ?Ingo
>
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