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Message-Id: <1194873980.7179.31.camel@twins>
Date: Mon, 12 Nov 2007 14:26:20 +0100
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: iozone write 50% regression in kernel 2.6.24-rc1
Single socket, dual core opteron, 2GB memory
Single SATA disk, ext3
x86_64 kernel and userland
(dirty_background_ratio, dirty_ratio) tunables
---- (5,10) - default
2.6.23.1-42.fc8 #1 SMP
524288 4 59580 60356
524288 4 59247 61101
524288 4 61030 62831
2.6.24-rc2 #28 SMP PREEMPT
524288 4 49277 56582
524288 4 50728 61056
524288 4 52027 59758
524288 4 51520 62426
---- (20,40) - similar to your 8GB
2.6.23.1-42.fc8 #1 SMP
524288 4 225977 447461
524288 4 232595 496848
524288 4 220608 478076
524288 4 203080 445230
2.6.24-rc2 #28 SMP PREEMPT
524288 4 54043 83585
524288 4 69949 516253
524288 4 72343 491416
524288 4 71775 492653
---- (60,80) - overkill
2.6.23.1-42.fc8 #1 SMP
524288 4 208450 491892
524288 4 216262 481135
524288 4 221892 543608
524288 4 202209 574725
524288 4 231730 452482
2.6.24-rc2 #28 SMP PREEMPT
524288 4 49091 86471
524288 4 65071 217566
524288 4 72238 492172
524288 4 71818 492433
524288 4 71327 493954
While I see that the write speed as reported under .24 ~70MB/s is much
lower than the one reported under .23 ~200MB/s, I find it very hard to
believe my poor single SATA disk could actually do the 200MB/s for
longer than its cache 8/16 MB (not sure).
vmstat shows that actual IO is done, even though the whole 512MB could
fit in cache, hence my suspicion that the ~70MB/s is the most realistic
of the two.
I'll have to look into what iozone actually does though and why this
patch makes the output different.
FWIW - because its a single backing dev it does get to 100% of the dirty
limit after a few runs, so not sure what makes the difference.
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