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    SubjectRe: Measuring tools - top and interrupts
    On 2006.06.24 18:23:12 +0200, Mike Galbraith wrote:
    > On Sat, 2006-06-24 at 17:40 +0200, Björn Steinbrink wrote:
    > > On 2006.06.24 13:41:57 +0200, Mike Galbraith wrote:
    > > > On Sat, 2006-06-24 at 11:52 +0200, Mike Galbraith wrote:
    > > > > On Sat, 2006-06-24 at 11:21 +0200, Björn Steinbrink wrote:
    > > > > >
    > > > > > The non-SMP call to update_process_times() is in do_timer_interrupt_hook(),
    > > > > > so I guess the above is not the Right Thing to do.
    > > > >
    > > > > Ah, there it is. That's what I was looking for. I figured that doing
    > > > > what I did had to be wrong, but tried it for grins anyway... was pretty
    > > > > surprised when it worked (kinda).
    > > >
    > > > Calling update_process_times() in do_timer_interrupt_hook() flat does
    > > > not work here. Calling it in smp_local_timer_interrupt() works fine.
    > > >
    > > > Oh joy.
    > >
    > > I can reproduce it now, seems to require CONFIG_4KSTACKS to fail. Can
    > > you confirm that?
    >
    > What a coincidence. After trying a different compiler, and slogging
    > through a bunch of assembler trying to figure out how the heck this can
    > happen, I was just booting an 8k stack kernel (as a wild-ass guess;).
    >
    > let's see. Yeah, confirmed.

    OK, it also depends on IO APIC being enabled and active, ie. noapic on
    the kernel command line will fix it as well as disabling
    CONFIG_X86_IO_APIC. That doesn't help me at all to understand why it
    happens though.
    The only difference with IO APIC disabled seems to be that the irq
    doesn't get ACKed before update_process_times() gets called.
    And your "fix" makes it being called outside of the xtime_lock spinlock
    and with a slightly different stack usage AFAICT.
    But none of these should make a difference, right?

    Björn
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