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Message-ID: <x494op25ntp.fsf@segfault.boston.devel.redhat.com>
Date: Tue, 10 Nov 2009 11:47:30 -0500
From: Jeff Moyer <jmoyer@...hat.com>
To: Corrado Zoccolo <czoccolo@...il.com>
Cc: Jan Kara <jack@...e.cz>, jens.axboe@...cle.com,
LKML <linux-kernel@...r.kernel.org>,
Chris Mason <chris.mason@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Galbraith <efault@....de>
Subject: Re: Performance regression in IO scheduler still there
Corrado Zoccolo <czoccolo@...il.com> writes:
> Jeff, Jens,
> do you think we should try to do more auto-tuning of cfq parameters?
> Looking at those numbers for SANs, I think we are being suboptimal in
> some cases.
> E.g. sequential read throughput is lower than random read.
I investigated this further, and this was due to a problem in the
benchmark. It was being run with only 500 samples for random I/O and
65536 samples for sequential. After fixing this, we see random I/O is
slower than sequential, as expected.
> I also think that current slice_idle and slice_sync values are good
> for devices with 8ms seek time, but they are too high for non-NCQ
> flash devices, where "seek" penalty is under 1ms, and we still prefer
> idling.
Do you have numbers to back that up? If not, throw a fio job file over
the fence and I'll test it on one such device.
> If we agree on this, should the measurement part (I'm thinking to
> measure things like seek time, throughput, etc...) be added to the
> common elevator code, or done inside cfq?
Well, if it's something that is of interest to others, than pushing it
up a layer makes sense. If only CFQ is going to use it, keep it there.
Cheers,
Jeff
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