Messages in this thread | | | Subject | Re: [patch] dubious process system time. | From | Martin Schwidefsky <> | Date | Thu, 24 Aug 2006 15:28:23 +0200 |
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On Thu, 2006-08-24 at 14:32 +0200, Andi Kleen wrote: > > The system time that is accounted to a process includes the time spent > > in three different contexts: normal system time, hardirq time and > > softirq time. To account hardirq time and sortirq time to a process > > seems wrong, because the process could just happen to run when the > > interrupt arrives that was caused by an i/o for a completly different > > process. And the sum over stime and cstime of all processes won't > > match cputstat->system either. > > The following patch changes the accounting of system time so that > > hardirq and softirq time are not accounted to a process anymore. > > So where does it get accounted then? It has to be accounted somewhere. > Sounds like a quite radical change to me, might break a lot of > existing assumptions.
At the moment hardirq+softirq is just added to a random process, in general this is completely wrong. You just need a system with a cpu hog and an i/o bound process and you get queer results. To add hardirq+softirq to a single process is wrong to begin with, for that you would need to be able to identify the process that caused the i/o. And if two processes require a single file page then what? Split the time required to load the page to two processes? Not really. The conclusion is that hardirq+softirq time should not be accouted to any process. It is accounted globally in cpustat->softirq and cpustat->hardirq.
There is one assumption that would break by the change: that the sum of the hardirq and softirq time is contained in the sum of the stime and cstime fields of all processes. I don't think that this is relevant.
-- blue skies, Martin.
Martin Schwidefsky Linux for zSeries Development & Services IBM Deutschland Entwicklung GmbH
"Reality continues to ruin my life." - Calvin.
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