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Date: Fri, 30 Oct 2009 10:02:27 +0800 From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> To: Mike Galbraith <efault@....de> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [patch] Re: hackbench regression with kernel 2.6.32-rc1 On Thu, 2009-10-29 at 10:14 +0100, Mike Galbraith wrote: > On Thu, 2009-10-29 at 14:26 +0800, Zhang, Yanmin wrote: > > On Thu, 2009-10-29 at 06:46 +0100, Mike Galbraith wrote: > > > > SD_PREFER_LOCAL is still on in rc1 though (double checks;), so you'll go > > > through the power saving code until you reach a domain containing both > > > waker's cpu and wakee's previous cpu even if that code already found > > > that a higher domain wasn't overloaded. Looks to me like that block > > > wants a want_sd && qualifier. > > > > > > Even it you turn SD_PREFER_LOCAL off, you can still hit the overhead if > > > SD_POWERSAVINGS_BALANCE is set, so I'd make sure both are off and see if > > > that's the source (likely, since the rest is already off). > > Yes. SD_POWERSAVINGS_BALANCE is disabled by default. I applied Peter's patch which > > turning SD_PREFER_LOCAL off for MC and cpu domain and it doesn't help. > > perf counter shows select_task_rq_fair still consumes about 5% cpu time. Eventually, > > I found for_each_cpu in for_each_domain consumes the 5% cpu time, because Peter's > > patch doesn't turn off SD_PREFER_LOCAL for node domain. > > I turned it off for node domain against the latest tips tree and tbench regression > > disappears on a Nehalem machine and becomes about 2% on another one. > > > > Can we turn it off for node domain by default? > > If it's hurting fast path overhead to the tune of an order of magnitude, > I guess there's no choice but to either fix it or turn it off. Since > SD_BALANCE_WAKE is off globally, I don't see any point in keeping > SD_PREFER_LOCAL at any level. > > (That said, what we need is for this to not be so expensive that we > can't afford it in the fast path). > > sched: Disable SD_PREFER_LOCAL at node level. > > Yanmin Zhang reported that SD_PREFER_LOCAL induces an order of magnitude > increase in select_task_rq_fair() overhead while running heavy wakeup > benchmarks (tbench and vmark). Since SD_BALANCE_WAKE is off at node level, > turn SD_PREFER_LOCAL off as well pending further investigation. Mike, Thanks a lot! With the patch, we do see much improvement on tbench and volanoMark. For exmaple, volanoMark has about 8% improvement with tips+the_patch, comparing with Kernel 2.6.31. Yanmin > > Signed-off-by: Mike Galbraith <efault@....de> > Cc: Ingo Molnar <mingo@...e.hu> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl> > Reported-by: Zhang, Yanmin <yanmin_zhang@...ux.intel.com> > LKML-Reference: <new-submission> > > diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h > index d823c24..40e37b1 100644 > --- a/arch/x86/include/asm/topology.h > +++ b/arch/x86/include/asm/topology.h > @@ -143,7 +143,7 @@ extern unsigned long node_remap_size[]; > | 1*SD_BALANCE_FORK \ > | 0*SD_BALANCE_WAKE \ > | 1*SD_WAKE_AFFINE \ > - | 1*SD_PREFER_LOCAL \ > + | 0*SD_PREFER_LOCAL \ > | 0*SD_SHARE_CPUPOWER \ > | 0*SD_POWERSAVINGS_BALANCE \ > | 0*SD_SHARE_PKG_RESOURCES \ > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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