From mboxrd@z Thu Jan 1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 41552] Performance of writing and reading from multiple drives
decreases by 40% when going from Linux Kernel 2.6.36.4 to 2.6.37 (and beyond)
Date: Tue, 23 Aug 2011 14:38:55 GMT
Message-ID: <201108231438.p7NEctlj014043@demeter1.kernel.org>
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https://bugzilla.kernel.org/show_bug.cgi?id=41552
--- Comment #10 from Anonymous Emailer 2011-08-23 14:38:52 ---
Reply-To: James.Bottomley@HansenPartnership.com
On Mon, 2011-08-22 at 21:07 +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:
> We were using the default CFQ scheduler. I will change it to deadline and see
> what happens. Also, we are not using a file system to perform the writes,
> rather we are sending SCSI commands directly to the devices, nor are we doing
> anything special to the disks with a device mapper. We simply write to each
> one on a different thread one sector at a time.
>
> I will attempt to get the trace and will add it if I can.
If you're just using a SG_IO type scsi command, then virtually nothing
we've done in block/scsi should affect this; certainly not the elevators
since we don't do merging on SG_IO, we just use them for queueing.
Since you say "write to each one on a different thread", it's possible
that some scheduler change may have impacted this.
James
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