linux-kernel - Re: [Bug #10638] sysbench+mysql(oltp, readonly) 30% regression with 2.6.26-rc1

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Date:	Thu, 05 Jun 2008 10:34:24 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [Bug #10638] sysbench+mysql(oltp, readonly) 30% regression
	with 2.6.26-rc1


On Wed, 2008-06-04 at 13:19 +0200, Ingo Molnar wrote:
> * Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> 
> > 
> > On Fri, 2008-05-30 at 11:45 +0200, Ingo Molnar wrote:
> > > Yanmin,
> > > 
> > > could you please check whether the performance regressions you 
> > > noticed are now fixed in upstream -git? [make sure merge 
> > > a7f75d3bed28 is included]
> > > 
> > > i believe most of the regressions to 2.6.25 you found should be 
> > > addressed - if not, please let me know which one is still hurting.
> >
> > Most regressions are fixed.
> 
> great - thanks for the exhaustive testing! In fact there should be nice 
> speedups in most of the categories as well ;-)
> 
> out of the 5 issues, only one is inconclusive:
> 
> > On 16-thread tulsa machine, hackbench result becomes 34 seconds. 
> > 2.6.26-rc2's result is 40 seconds and 2.6.26-rc1's is 30 seconds. So 
> > there is much improvement. On another Montvale machine(supporting 
> > multi-threading, but I don't turn on it in BIOS), hackbench has the 
> > similiar behavior.
> 
> okay, that's "hackbench 100", which creates a swarm of 2000 runnable 
> tasks and which is extremely sensitive to wakeup preemption details. It 
> is a volanomark work-alike, so if volanomark itself works fine (which it 
> does appear, from your other numbers) and this one regresses a bit, i'm 
> not sure there's anything fundamental to be worried about.
One difference between volanoMark and hackbench is cpu context switch.
cpu context switch looks stable when I run volanoMark, but dones't look
stable with hackbench.

running queue is another difference. With volanoMark, running queue is quite stable.
With hackbench, running queue keeps decreasing, sometimes quickly, sometimes slowly.

> 
> Quite likely you'll get more stable results if you run it all batched 
> (which such workload really should):
> 
>  schedtool -B -e hackbench 100
I tested it by #hackbench process 2000 with/without schedtool.

If I don't kill most background processes (services), the result is still not stable.
If I kill background processes, the fluctuation is within 0.5 seconds
with or without schedtool. It looks like -B makes the result a little better, but
very little about 1 second.

> 
> right?
> 
> the 16-thread tulsa machine, how is it laid out physically: 2 sockets, 4 
> cores per socket, 2 threads per core?
4 sockets, 2 cores per socket, 2 threads per core.


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