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    SubjectRe: >10% performance degradation since 2.6.18
    On Fri, Jul 03 2009, Matthew Wilcox wrote:
    > On Fri, Jul 03, 2009 at 08:54:14PM +0200, Jens Axboe wrote:
    > > On Fri, Jul 03 2009, Andi Kleen wrote:
    > > >
    > > > Matthew Wilcox <matthew@wil.cx> writes:
    > > > >
    > > > > ======oprofile CPU_CLK_UNHALTED for top 30 functions
    > > > > Cycles% 2.6.18-92.el5-op Cycles% 2.6.30
    > > > > 70.1409 <database> 67.0207 <database>
    > > > > 1.3556 mpt_interrupt 1.7029 mpt_interrupt
    > > >
    > > > It's strange that mpt_interrupt is that more costly in 2.6.30
    > > > than in 2.6.18. I diffed 2.6.30's drivers/message/fusion/mptbase.c
    > > > to a rhel 5.3s and they seem to be about the same.
    > > >
    > > > So why does it cost 0.5% more in 2.6.30?
    > > >
    > > > [adding MPT maintainers]
    > >
    > > Look at the irqs/sec rate, it's higher by about the same percentage. So
    > > it's likely not a more costly irq handler, it's likely just called that
    > > much more. It could be IO pattern, causing more commands to be issued
    > > (which leads to more interrupts, etc).
    >
    > Yes, but the irqs/sec increase doesn't appear to be due to MPT interrupts.
    > In the /proc/interrupt summaries, RH5 did 388666895 IOC interrupts and
    > 2.6.30 did 378419042. As a percentage of interrupts, the IOC interrupts
    > were 59.4% with RH and 51.8% with 2.6.30.

    OK. So where are the extra irqs from?

    > This isn't quite conclusive since the collection of /proc/interrupts is
    > over the entire life of the system, not during the measurement period.
    > But I do find it persuasive.

    Since the total is so high, it's probably good enough and sampling only
    during the measurement likely wouldn't change that picture a lot.

    --
    Jens Axboe



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