linux-kernel - Re: [PATCH 2/2] block: account iowait time when waiting for completion of IO request

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Date:	Fri, 15 Feb 2013 16:44:21 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, devel@...nvz.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] block: account iowait time when waiting for
 completion of IO request

On Thu, Feb 14 2013, Vladimir Davydov wrote:
> Using wait_for_completion() for waiting for a IO request to be executed
> results in wrong iowait time accounting. For example, a system having
> the only task doing write() and fdatasync() on a block device can be
> reported being idle instead of iowaiting as it should because
> blkdev_issue_flush() calls wait_for_completion() which in turn calls
> schedule() that does not increment the iowait proc counter and thus does
> not turn on iowait time accounting.
> 
> The patch makes block layer use wait_for_completion_io() instead of
> wait_for_completion() where appropriate to account iowait time
> correctly.

Thanks, applied both for 3.9 (with Ingos ack).

-- 
Jens Axboe

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