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To: Ingo Molnar <mingo@elte.hu>
cc: Jan Kara <jack@suse.cz>, Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: updated: ext3 IO latency measurements on v2.6.30-rc1 
In-Reply-To: Your message of "Thu, 09 Apr 2009 23:59:46 +0200."
             <20090409215946.GA28183@elte.hu> (sfid-20090515_115729_335569_6D25DDD8) 
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Date: Mon, 18 May 2009 12:37:19 -0400
From: Sanjoy Mahajan <sanjoy@mit.edu>
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To test the ext3 improvements in 2.6.30-rc5, I tried my previous test of
starting an rxvt while findutils or 'aptitude dist-upgrade' is madly
spinning the disk.

With vanilla 2.6.29 in those circumstances, starting an rxvt took 4
seconds on an otherwise unloaded system (Thinkpad T60 w/ 1.83GHz
dual-core CPU, 1.5GB RAM, 5400 rpm drive).  The second rxvt came up
right away.  So the first rxvt probably stalled until /usr/bin/rxvt
could be grabbed from disk.

With 2.6.30-rc5, the rxvt showed up much faster -- either right away
(maybe it was still in the cache) or after about 0.5 seconds (probably
the uncached case).

Other tests were also snappy, like opening a 10MB PDF file in Emacs,
adding a newline at the beginning, and saving it (while findutils was
running).  I hadn't done the same test with 2.6.29, but I'm pretty sure
it would have been painfully slow if findutils was running.

So, relative to 2.6.29, I see a large improvement in interactive
behavior under high IO load.

-Sanjoy

`Until lions have their historians, tales of the hunt shall always
 glorify the hunters.'  --African Proverb