[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)

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=41552





--- Comment #10 from Anonymous Emailer <anonymous@kernel-bugs.osdl.org>  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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