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Date: Tue, 1 Oct 2002 14:30:13 +0200
From: Jens Axboe <axboe@suse.de>
To: Con Kolivas <conman@kolivas.net>
Cc: Andrew Morton <akpm@digeo.com>,
       linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: [BENCHMARK] 2.5.39-mm1
Message-ID: <20021001123013.GS3867@suse.de>
References: <200209301941.41627.conman@kolivas.net> <20021001101520.GB20878@suse.de> <3D9976D9.C06466B@digeo.com> <200210012219.53464.conman@kolivas.net>
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On Tue, Oct 01 2002, Con Kolivas wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On Tuesday 01 Oct 2002 8:20 pm, Andrew Morton wrote:
> > Jens Axboe wrote:
> > > On Mon, Sep 30 2002, Andrew Morton wrote:
> > > > > io_load:
> > > > > Kernel                  Time            CPU             Ratio
> > > > > 2.4.19                  216.05          33%             3.19
> > > > > 2.5.38                  887.76          8%              13.11
> > > > > 2.5.38-mm3              105.17          70%             1.55
> > > > > 2.5.39                  229.4           34%             3.4
> > > > > 2.5.39-mm1              239.5           33%             3.4
> > > >
> > > > I think I'll set fifo_batch to 16 again...
> > >
> > > As not to compare oranges and apples, I'd very much like to see a
> > > 2.5.39-mm1 vs 2.5.39-mm1 with fifo_batch=16. Con, would you do that?
> > > Thanks!
> >
> > The presence of /proc/sys/vm/fifo_batch should make that pretty easy.
> 
> Thanks. That made it a lot easier and faster, and made me curious enough to 
> create a family or very interesting results. All these are with 2.5.39-mm1 
> with fifo_batch set to 1->16, average of three runs. The first result is the 
> unmodified 2.5.39-mm1 (fifo_batch=32).

Ah excellent, thanks a lot!

> io_load:
> Kernel                  Time            CPU%            Ratio
> 2.5.39-mm1              239.5           32              3.54
> 2539mm1fb16             131.2           57              1.94
> 2539mm1fb8              109.1           68              1.61
> 2539mm1fb4              146.4           51              2.16
> 2539mm1fb2              112.7           65              1.67
> 2539mm1fb1              125.4           60              1.85
> 
> What's most interesting is the variation was small until the number was <8; 
> then the variation between runs increased. Dare I say it there appears to be 
> a sweet spot in the results.

Yes it's an interesting curve. What makes it interesting is that 8 is
better than 16. Both allow one seek to be dispatched, they only differ
in the streamed amount of data we allow to dispatch. 8 will give you
either 1 seek, or 8*256 == 2048 sectors == 1MiB. 16 will give you 1 seek
or 2MiB of streamed I/O.

Tests with other io benchmarks need to be considered as well. And I need
a bit of time to digest this :-). The 8 vs 16 numbers are not what I
expected.

But the deadline io scheduler looks damn good in this test, if I have to
say so myself.

-- 
Jens Axboe

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