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From: Ingo Molnar <mingo@elte.hu>
To: Divyesh Shah <dpshah@google.com>
Cc: jaxboe@fusionio.com, peterz@infradead.org, piotr@hosowicz.com,
	linux-kernel@vger.kernel.org, vgoyal@redhat.com,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio cgroup stats.
Date: Sat, 12 Jun 2010 09:18:47 +0200	[thread overview]
Message-ID: <20100612071847.GA29751@elte.hu> (raw)
In-Reply-To: <20100612023457.14850.50439.stgit@austin.mtv.corp.google.com>


* 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.

	Ingo

  reply	other threads:[~2010-06-12  7:19 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-06-12  2:34 [PATCH 1/2] Remove preempt_enable/disable calls around sched_clock() Divyesh Shah
2010-06-12  2:35 ` [PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio cgroup stats Divyesh Shah
2010-06-12  7:18   ` Ingo Molnar [this message]
2010-06-12 15:51     ` Divyesh Shah
2010-06-12  7:19 ` [PATCH 1/2] Remove preempt_enable/disable calls around sched_clock() Ingo Molnar
2010-06-12 15:52   ` Divyesh Shah
2010-06-13 10:01     ` Ingo Molnar

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