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Date: Thu, 16 May 2002 00:41:36 -0700
From: Andrew Morton <akpm@zip.com.au>
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CC: Rik van Riel <riel@conectiva.com.br>, linux-kernel@vger.kernel.org,
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Subject: Re: [RFC][PATCH] iowait statistics
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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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