linux-kernel - Re: SATA Harddisk speed drop of 100 MB/s

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Date:	Sat, 23 Jun 2007 04:59:06 +0200
From:	Carlo Wood <carlo@...noe.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Jeff Garzik <jeff@...zik.org>, linux-kernel@...r.kernel.org
Subject: Re: SATA Harddisk speed drop of 100 MB/s

On Fri, Jun 22, 2007 at 10:31:32PM -0300, Henrique de Moraes Holschuh wrote:
> for i in /sys/block/sd*/queue/scheduler ; do echo -n "scheduler for $i was:" ; cat $i ; echo anticipatory > $i ; done
> 
> Should show you the scheduler for all libata/scsi discs, and switch to
> anticipatory.  It probably works for hd* as well, but I don't have any
> around to test.
> 
> I had ridiculous md raid performance (on resync) using cfq at least once.
> Unfortunately I never bothered trying to track it down, and I didn't check
> the throughput after the resync was done either. Also, I don't recall the
> kernel version, but it was either 2.6.18 or 2.6.20.

Just one kernel version? The problem here is in every
kernel revision after 551c012d7eea3dc5ec063c7ff9c718d39e77634f

2.6.20-rc2,rc3,rc4,rc5,rc6,rc7 ... 2.6.20 ... 2.6.21 ... 2.6.22-rc5

noop:
 Timing buffered disk reads:  254 MB in  3.00 seconds =  84.66 MB/sec

anticipatory:
 Timing buffered disk reads:  252 MB in  3.02 seconds =  83.43 MB/sec

deadline:
 Timing buffered disk reads:  258 MB in  3.02 seconds =  85.41 MB/sec

cfq:
 Timing buffered disk reads:  194 MB in  3.03 seconds =  64.06 MB/sec

The normal value is cfq. So, all other schedulars are somewhat faster,
but still far from the correct 165 MB/s.

-- 
Carlo Wood <carlo@...noe.com>
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