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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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