|To:||Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>|
|Subject:||Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs]|
|From:||Bill Davidsen <davidsen@xxxxxxx>|
|Date:||Wed, 10 Dec 2008 19:20:37 -0500|
|Cc:||linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Alan Piszcz <ap@xxxxxxxxxxxxx>|
|Organization:||TMR Associates Inc, Schenectady NY|
|User-agent:||Mozilla/5.0 (X11; U; Linux i686; en-US; rv:126.96.36.199) Gecko/20081112 Fedora/1.1.13-1.fc9 SeaMonkey/1.1.13|
Justin Piszcz wrote:
Someone should write a document with XFS and barrier support, if I recall,I would expect you, as an experienced tester, to have done this measurement more rigorously!
I don't think it means much if this is what you did.
l1:~# /usr/bin/time tar xf linux-188.8.131.52.tar 0.15user 1.54system 0:13.18elapsed 12%CPU (0avgtext+0avgdata 0maxresident)kBefore doing any disk test you need to start by dropping cache, to be sure the appropriate reproducible things happen. And in doing a timing test, you need to end with a sync for the same reason.
So: echo 1 >/proc/sys/vm/drop_caches time bash -c "YOUR TEST; sync"
This will give you a fair shot at being able to reproduce the results, done on an otherwise unloaded system.
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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