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    SubjectRe: high system cpu load during intense disk i/o

    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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      Last update: 2007-08-06 20:31    [W:0.020 / U:3.892 seconds]
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