Messages in this thread | | | Date | Tue, 21 Oct 2008 13:58:02 +0200 | From | "Zdenek Kabelac" <> | Subject | Re: Scheduler on C2D CPU and latest 2.6.27 kernel |
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2008/10/21 Chris Snook <csnook@redhat.com>: > Zdenek Kabelac wrote: >> >> 2008/10/21 Chris Snook <csnook@redhat.com>: >>> >>> Zdenek Kabelac wrote: >>>> >>>> Hi >>>> >>>> Recently I'm noticing bad behavior of the CPU scheduler on my T61 (2GB, >>>> C2D) >>>> >>>> It looks like Linux concentrates all running tasks on one CPU and the >>>> second cpu is sleeping. >>>> >>>> With recent changes to DRI - glxgears went up to 840FPS but also takes >>>> 100% (with Xorg) and when I run 'while :; do true; done' loop in >>>> parallel frame rate drops to 300FPS. >>>> >>>> But as I have C2D CPU I would expect that there should be no such >>>> dramatic slowdown. >>>> >>>> Xosview shows that only one CPU is fully loaded. >>>> >>>> Here are my .config scheduler options: >>>> >>>> CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y >>>> # CONFIG_GROUP_SCHED is not set >>>> CONFIG_IOSCHED_NOOP=y >>>> CONFIG_IOSCHED_AS=y >>>> CONFIG_IOSCHED_DEADLINE=y >>>> CONFIG_IOSCHED_CFQ=y >>>> CONFIG_DEFAULT_IOSCHED="cfq" >>>> CONFIG_SCHED_SMT=y >>>> # CONFIG_SCHED_MC is not set >> >> I've also tested SMT=n MC=y - with same result > > Expected. > >>>> CONFIG_SCHED_HRTICK=y >>>> # CONFIG_NET_SCHED is not set >>>> CONFIG_USB_EHCI_TT_NEWSCHED=y >>>> CONFIG_SCHED_DEBUG=y >>>> CONFIG_SCHEDSTATS=y >>>> CONFIG_SCHED_TRACER=y >>>> >>>> >>>> Am I missing something? >>> >>> You're running a loop that does nothing except create new tasks that have >>> no >>> scheduling history, and then disappear before the scheduler can migrate >>> them. >>> >>> Try running 'openssl speed' to chew up CPU. I promise you the scheduler >>> will behave very nicely. >> >> Well - sorry you really shouldn't promise things you cannot guarantee. > > You must be new here.
hmm, I don't think so :)
> >> It's obviously showing exactly same problem on my box. > > If you start 2 'openssl speed' tasks while glxgears is running, what > happens? > >> And I should add that with 2.6.27-rc8 I do not experience this behavior. > > Thanks. Can you bisect?
Maybe the author of this regression will 'confess' himself and will safe my time?
I can see some major merge on Oct 20 for kernel/sched.c
> >> Gears are showning 80% speed - but consumes only 25% >> and bash loop or openssl speed task do not influence its speed. >> (as expected with 2CPU machine) > > That's definitely what it should be doing with openssl speed. The bash loop > isn't something we should go out of our way to optimize for, since real > world apps don't behave that way, but if there's a free fix, we might as > well do it.
You really should check first what the loop I've posted actually does :) (hint - /bin/true != true)
Zdenek
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