Re: iozone write 50% regression in kernel 2.6.24-rc1

[Martin Knoblauch <knobi@knobisoft.de>]

----- Original Message ----
> From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
> To: a.p.zijlstra@chello.nl
> Cc: LKML <linux-kernel@vger.kernel.org>
> Sent: Friday, November 9, 2007 10:47:52 AM
> Subject: iozone write 50% regression in kernel 2.6.24-rc1
> 
> Comparing with 2.6.23, iozone sequential write/rewrite (512M) has
> 50%
> 
 regression
> in kernel 2.6.24-rc1. 2.6.24-rc2 has the same regression.
> 
> My machine has 8 processor cores and 8GB memory.
> 
> By bisect, I located patch
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=
> 04fbfdc14e5f48463820d6b9807daa5e9c92c51f.
> 
> 
> Another behavior: with kernel 2.6.23, if I run iozone for many
> times
> 
 after rebooting machine,
> the result looks stable. But with 2.6.24-rc1, the first run of
> iozone
> 
 got a very small result and
> following run has 4Xorig_result.
> 
> What I reported is the regression of 2nd/3rd run, because first run
> has
> 
 bigger regression.
> 
> I also tried to change
> /proc/sys/vm/dirty_ratio,dirty_backgroud_ratio
> 
 and didn't get improvement.
> 
> -yanmin
> -
Hi Yanmin,

 could you tell us the exact iozone command you are using? I would like to repeat it on my setup, because I definitely see the opposite behaviour in 2.6.24-rc1/rc2. The speed there is much better than in 2.6.22 and before (I skipped 2.6.23, because I was waiting for the per-bdi changes). I definitely do not see the difference between 1st and subsequent runs. But then, I do my tests with 5GB file sizes like:

iozone3_283/src/current/iozone -t 5 -F /scratch/X1 /scratch/X2 /scratch/X3 /scratch/X4 /scratch/X5 -s 5000M -r 1024 -c -e -i 0 -i 1

Kind regards
Martin