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    SubjectRe: [RFC][PATCH] iowait statistics
    Denis Vlasenko wrote:
    >
    > On 14 May 2002 00:18, Andrew Morton wrote:
    > > Rik van Riel wrote:
    > > > 4) on SMP systems the iowait time can be overestimated, no big
    > > > deal IMHO but cheap suggestions for improvement are welcome
    > >
    > > I suspect that a number of these statistical accounting mechanisms
    > > are going to break. The new irq-affinity code works awfully well.
    > >
    > > The kernel profiler in 2.5 doesn't work very well at present.
    > > When investigating this, I ran a busy-wait process. It attached
    > > itself to CPU #3 and that CPU received precisely zero interrupts
    > > across a five minute period. So the profiler cunningly avoids profiling
    > > busy CPUs, which is rather counter-productive. Fortunate that oprofile
    > > uses NMI.
    >
    > What, even local APIC interrupts did not happen on CPU#3
    > in these five mins?

    CPU1 is busy:

    quad:/home/akpm> cat /proc/interrupts ; sleep 10 ; cat /proc/interrupts
    CPU0 CPU1 CPU2 CPU3
    0: 36059 33847 38948 33846 IO-APIC-edge timer
    1: 1 1 1 4 IO-APIC-edge keyboard
    2: 0 0 0 0 XT-PIC cascade
    4: 1 1 1 0 IO-APIC-edge GDB-stub
    8: 0 0 0 1 IO-APIC-edge rtc
    12: 0 1 0 0 IO-APIC-edge PS/2 Mouse
    14: 1 2 0 3 IO-APIC-edge ide0
    15: 7558 7557 7633 8025 IO-APIC-edge ide1
    19: 17088 17707 17210 18610 IO-APIC-level ide2, ide3, ide4, ide5
    35: 38 71 56 174 IO-APIC-level aic7xxx
    38: 955 1798 584 517 IO-APIC-level eth0
    58: 25368 19911 27931 20695 IO-APIC-level aic7xxx
    NMI: 164030 164030 164030 164030
    LOC: 142543 142543 142542 142542
    ERR: 0
    MIS: 0
    CPU0 CPU1 CPU2 CPU3
    0: 36388 33847 39289 34178 IO-APIC-edge timer
    1: 1 1 1 4 IO-APIC-edge keyboard
    2: 0 0 0 0 XT-PIC cascade
    4: 1 1 1 0 IO-APIC-edge GDB-stub
    8: 0 0 0 1 IO-APIC-edge rtc
    12: 0 1 0 0 IO-APIC-edge PS/2 Mouse
    14: 1 2 0 3 IO-APIC-edge ide0
    15: 7565 7557 7633 8026 IO-APIC-edge ide1
    19: 17088 17707 17210 18610 IO-APIC-level ide2, ide3, ide4, ide5
    35: 38 71 56 174 IO-APIC-level aic7xxx
    38: 969 1798 590 525 IO-APIC-level eth0
    58: 25368 19911 27931 20695 IO-APIC-level aic7xxx
    NMI: 165032 165032 165032 165032
    LOC: 143545 143545 143544 143544
    ERR: 0
    MIS: 0


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