On Mon, 2007-11-12 at 04:58 -0800, Martin Knoblauch wrote:
> ----- Original Message ----
> > From: "Zhang, Yanmin" <[email protected]>
> > To: Martin Knoblauch <[email protected]>
> > Cc: [email protected]; LKML <[email protected]>
> > Sent: Monday, November 12, 2007 1:45:57 AM
> > Subject: Re: iozone write 50% regression in kernel 2.6.24-rc1
> >
> > On Fri, 2007-11-09 at 04:36 -0800, Martin Knoblauch wrote:
> > > ----- Original Message ----
> > > > From: "Zhang, Yanmin"
> > > > To: [email protected]
> > > > Cc: LKML
> > > > 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.
> > > could you tell us the exact iozone command you are using?
> > iozone -i 0 -r 4k -s 512m
> >
>
> OK, I definitely do not see the reported effect. On a HP Proliant with a RAID5 on CCISS I get:
>
> 2.6.19.2: 654-738 MB/sec write, 1126-1154 MB/sec rewrite
> 2.6.24-rc2: 772-820 MB/sec write, 1495-1539 MB/sec rewrite
>
> The first run is always slowest, all subsequent runs are faster and the same speed.
Although the first run is always slowest, but if we compare 2.6.23 and 2.6.24-rc,
we could find the first run result of 2.6.23 is 7 times of the one of 2.6.24-rc.
Originally, my test suite is just to pick up the result of first run. I might
change my test suite to make it run for many times.
Now I run the the test manually for many times after machine reboots. Comparing 2.6.24-rc
with 2.6.23, 3rd and following run of 2.6.24-rc has about 50% regression.
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