Date: Fri, 27 Nov 2009 09:23:16 +0100
From: Jens Axboe <jens.axboe@oracle.com>
To: Corrado Zoccolo <czoccolo@gmail.com>
Cc: Linux-Kernel <linux-kernel@vger.kernel.org>,
       Jeff Moyer <jmoyer@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
       mel@csn.ul.ie, efault@gmx.de
Subject: Re: [RFC,PATCH] cfq-iosched: improve async queue ramp up formula
Message-ID: <20091127082316.GY8742@kernel.dk>
References: <200911261710.40719.czoccolo@gmail.com>
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On Thu, Nov 26 2009, Corrado Zoccolo wrote:
> The introduction of ramp-up formula for async queue depths has
> slowed down dirty page reclaim, by reducing async write performance.
> This patch improves the formula by considering the remaining slice.
> 
> The new formula will allow more dispatches at the beginning of the
> slice, reducing them at the end.
> This will ensure that we achieve good throughput, without the risk of
> overrunning the allotted timeslice.
> 
> The threshold is automatically increased when sync I/O is not
> intermingled with async, in accordance with the previous incarnation of
> the formula.

The slow ramp up is pretty much essential to being able to have low
latency for the sync reads, so I'm afraid this will break that. I would
prefer doing it through memory reclaim detection, like the other patch
you and Motohiro suggested.

-- 
Jens Axboe

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