linux-kernel - Re: [RFC PATCH] block: Fix bio merge induced high I/O latency

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Message-ID: <807b3a220901190745w79827b41u1cc9045a2ac268e5@mail.gmail.com>
Date:	Mon, 19 Jan 2009 21:15:56 +0530
From:	Nikanth K <nikanth@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Andrea Arcangeli <andrea@...e.de>, akpm@...ux-foundation.org,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, ltt-dev@...ts.casi.polymtl.ca
Subject: Re: [RFC PATCH] block: Fix bio merge induced high I/O latency

On Sun, Jan 18, 2009 at 12:34 AM, Jens Axboe <jens.axboe@...cle.com> wrote:

>
> As a quick test, could you try and increase the slice_idle to eg 20ms?
> Sometimes I've seen timing being slightly off, which makes us miss the
> sync window for the ls (in your case) process. Then you get a mix of
> async and sync IO all the time, which very much slows down the sync
> process.
>

Do you mean to say that 'ls' could not submit another request until
the previous sync request completes, but its idle window gets disabled
as it takes way too long to complete during heavy load? But when there
are requests in the driver, wont the idling be disabled anyway? Or did
you mean to increase slice_sync?

Thanks
Nikanth
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