linux-kernel - Re: UDP-U stream performance regression on 32-rc1 kernel

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Date:	Thu, 05 Nov 2009 06:20:17 +0100
From:	Mike Galbraith <efault@....de>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>, alex.shi@...el.com,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: UDP-U stream performance regression on 32-rc1 kernel

On Thu, 2009-11-05 at 10:20 +0800, Zhang, Yanmin wrote:
> On Wed, 2009-11-04 at 13:07 +0100, Mike Galbraith wrote:

> > Can you try the below, and send me 
> I tested it on Nehalem machine against the latest tips kernel. netperf loopback
> result is good and regression disappears.

Excellent.  Ingo has picked up a version in tip (1b9508f) which has zero
negative effect on my x264 testcase, and is a win for mysql+oltp through
the whole test spectrum.  As that may (dunno, Ingo?) now be considered a
regression fix, ie candidate for 32.final, testing that it does no harm
to your big machines would be a good thing.  (pretty please?:)

> tbench result has no improvement.

Can you remind me where we stand on tbench?

> > your UDP-U-1k args so I can try it? 
> #taskset -c 0 ./netserver
> #taskset -c 15 ./netperf -t UDP_STREAM -l 60 -H 127.0.0.1 -i 50 3 -I 99 5 -- -P 12384,12888 -s 32768 -S 32768 -m 4096
> 
> Pls. check /proc/cpuinfo to make sure cpu 0 and cpu 15 are not in the
> same physical cpu.

Thanks. My little box doesn't have a 15 (darn) so 0,3 will have to do.

> I also run sysbench(oltp)+mysql testing with thread number 14,16,18,20,32,64,128. The average
> number is good. If I compare every single result against 2.6.32-rc5's, I find thread number
> 14,16,18,20,32's result are better than 2.6.32-rc5's, but 64,128's result are worse. 128's is
> the worst.

Hm.  That's disconcerting.  However, that patch isn't going anywhere but
to the bitwolf anyway (diagnostic).  If 1b9508f regresses, that will be
a problem.  With diag, my box also regressed at the tail.  Balancing a
bit seems to help mysql once it starts tripping all over itself, it
improves the decay curve markedly.  1b9508f does brief bursts of newidle
balancing when idle time climbs, which translated to a ~6% improvement
at 256 clients on my little quad.

	-Mike

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