Messages in this thread | | | Date | Mon, 06 Aug 2007 21:27:56 +0200 | From | Dimitrios Apostolou <> | Subject | Re: high system cpu load during intense disk i/o |
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Hi,
Andrew Morton wrote: > I suspect I was fooled by the oprofile output, which showed tremendous > amounts of load in schedule() and switch_to(). The percentages which > opreport shows are the percentage of non-halted CPU time. So if you have a > function in the kernel which is using 1% of the total CPU, and the CPU is > halted for 95% of the time, it appears that the function is taking 20% of > CPU! > > The fix for that is to boot with the "idle=poll" boot parameter, to make > the CPU spin when it has nothing else to do.
I'll test again the two_discs_bad situation after booting with that parameter. Thanks.
> > I'm suspecting that your machine is just stuck in D state waiting for disk. > Did we have a sysrq-T trace?
The amazing thing is that this doesn't happen! Every single cron jobs that keeps running (I intentionally said that before too) and never ends is in R state. By strace'ing the processes they just seem to be going *extremely* slow. I also changed the I/O elevator of hdb (the OS disk) to deadline from cfq, unfortunately with no results. That is why I 've been considering it a CPU scheduler issue.
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