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    SubjectRe: [tbench regression fixes]: digging out smelly deadmen.

    * Evgeniy Polyakov <s0mbre@tservice.net.ru> wrote:

    > Hi Ingo.
    >
    > On Fri, Oct 10, 2008 at 11:15:11AM +0200, Ingo Molnar (mingo@elte.hu) wrote:
    >
    > > >
    > > > I use tsc clocksource, also available acpi_pm and jiffies,
    > > > with acpi_pm performance is even lower (I stopped test after it dropped
    > > > below 340 MB/s mark), jiffies do not work at all, looks like sockets
    > > > stuck in time_wait state when this clock source is used, although that
    > > > may be some different issue.
    > > >
    > > > So I think hrticks are guilty, but still not as good as .25 tree without
    > > > mentioned changes (455 MB/s) and .24 (475 MB/s).
    > >
    > > i'm glad that you are looking into this! That is an SMP box, right? If
    > > yes then could you try this sched-domains tuning utility i have written
    > > yesterday (incidentally):
    > >
    > > http://redhat.com/~mingo/cfs-scheduler/tune-sched-domains
    >
    > I've removed SD_BALANCE_NEWIDLE:
    > # ./tune-sched-domains $[191-2]
    > changed /proc/sys/kernel/sched_domain/cpu0/domain0/flags: 191 => 189
    > SD flag: 189
    > + 1: SD_LOAD_BALANCE: Do load balancing on this domain
    > - 2: SD_BALANCE_NEWIDLE: Balance when about to become idle
    > + 4: SD_BALANCE_EXEC: Balance on exec
    > + 8: SD_BALANCE_FORK: Balance on fork, clone
    > + 16: SD_WAKE_IDLE: Wake to idle CPU on task wakeup
    > + 32: SD_WAKE_AFFINE: Wake task to waking CPU
    > - 64: SD_WAKE_BALANCE: Perform balancing at task wakeup
    > + 128: SD_SHARE_CPUPOWER: Domain members share cpu power
    > changed /proc/sys/kernel/sched_domain/cpu0/domain1/flags: 47 => 189
    > SD flag: 189
    > + 1: SD_LOAD_BALANCE: Do load balancing on this domain
    > - 2: SD_BALANCE_NEWIDLE: Balance when about to become idle
    > + 4: SD_BALANCE_EXEC: Balance on exec
    > + 8: SD_BALANCE_FORK: Balance on fork, clone
    > + 16: SD_WAKE_IDLE: Wake to idle CPU on task wakeup
    > + 32: SD_WAKE_AFFINE: Wake task to waking CPU
    > - 64: SD_WAKE_BALANCE: Perform balancing at task wakeup
    > + 128: SD_SHARE_CPUPOWER: Domain members share cpu power
    >
    > And got noticeble improvement (each new line has fixes from previous):
    >
    > vanilla 27: 347.222
    > no TSO/GSO: 357.331
    > no hrticks: 382.983
    > no balance: 389.802
    >
    > > and please, when tuning such scheduler bits, could you run latest
    > > tip/master:
    > >
    > > http://people.redhat.com/mingo/tip.git/README
    > >
    > > and you need to have CONFIG_SCHED_DEBUG=y enabled for the tuning knobs.
    > >
    > > so that it's all in sync with upcoming scheduler changes/tunings/fixes.
    >
    > Ok, I've started to pull it down, I will reply back when things are
    > ready.

    make sure you have this fix in tip/master already:

    5b7dba4: sched_clock: prevent scd->clock from moving backwards

    Note: Mike is 100% correct in suggesting that a very good cpu_clock() is
    needed for precise scheduling.

    i've also Cc:-ed Nick.

    Ingo


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