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Date: Mon, 5 Nov 2001 08:06:35 +0100
From: Jens Axboe <axboe@suse.de>
To: Andrew Morton <akpm@zip.com.au>
Cc: Mike Fedyk <mfedyk@matchmail.com>, lkml <linux-kernel@vger.kernel.org>,
        ext2-devel@lists.sourceforge.net
Subject: Re: [Ext2-devel] disk throughput
Message-ID: <20011105080635.D2580@suse.de>
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On Sun, Nov 04 2001, Andrew Morton wrote:
> The meaning of the parameter to elvtune is a complete mystery, and the
> code is uncommented crud (tautology).  So I just used -r20000 -w20000.

It's the number of sectors that are allowed to pass a request on the
queue, because of merges or inserts before that particular request. So
you want lower than that probably, and you want READ latency to be
smaller than WRITE latency too. The default I set is 8192/16384 iirc, so
go lower than this -- -r512 -w1024 or even lower just to check the
results.

> This was based on observing the request queue dynamics.  We frequently
> fail to merge requests which really should be merged regardless of
> latency.  Bumping the elvtune settings fixed it all.  But once the
> fs starts writing data out contiguously it's all academic.

Interesting, the 2.5 design prevents this since it doesn't account
merges as a penalty (like a seek). I can do something like that for 2.4
too, I'll do a patch for you to test.

-- 
Jens Axboe

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