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    SubjectRe: 2.6.4 : 100% CPU use on EIDE disk operarion, VIA chipset
    Date
    Andreas Hartmann wrote:
    > Mikhail Ramendik wrote:
    >
    >> Hello,
    >>
    >> I have an computer with an AMD Duron, and the motehrboard chipset is VIA
    >> KT133. The hard drive is a Seagate Barracuda 7200.7 ; no other EIDE
    >> devices are attached.
    >>
    >> I run an RH9-based distro, and added a 2.6.4 kernel to it. The following
    >> problem was tested with two kernel variants: 2.6.4+wolk2/0 with
    >> preeemption enabled, and 2.6.4 plain from kernel.org with preemption
    >> disabled. No difference.
    >>
    >> I noticed performance problems with 2.6.4, and tracked them to strange
    >> HDD behavior.
    >>
    >> It turned out that on disk-intensive operation, the "system" CPU usage
    >> skyrockets. With a mere "cp" of a large file to the same direstory
    >> (tested with ext3fs and FAT32 file systems), it is 100% practically all
    >> of the time !
    >
    >
    > Which tool do you use for measure? xosview?
    >
    > I'm having here the same problem. But it depends on the tool which is
    > used for measuring. If I use top from procps 3.2, I can't see this high
    > system load. "time" can't see it, too.
    >
    > This is what top says during cp of 512MB-file:
    > Cpu(s): 2.0% us, 8.3% sy, 0.0% ni, 0.0% id, 89.0% wa, 0.7% hi,
    > 0.0% si
    >
    > New is "wa", what probably means "wait". This value is very high as long
    > as the HD is writing or reading datas:
    >
    > cp dummy /dev/null
    > produces this top-line:
    > Cpu(s): 3.0% us, 5.3% sy, 0.0% ni, 0.0% id, 91.0% wa, 0.7% hi,
    > 0.0% si

    Yes "wa" is not intuitive, some other operating systems use "wio" for
    "wait i/o" time. As noted in the other thread, you can try the deadline
    elevator or increased readahead for your load.
    >
    > and time says:
    > real 0m53.195s
    > user 0m0.013s
    > sys 0m2.124s
    >
    >
    > But you're right, 2.6.4 is slower than 2.4.25. See the thread "Very poor
    > performance with 2.6.4" here in the list.

    Much discussed, not overly fixed :-(

    --
    bill davidsen <davidsen@tmr.com>
    CTO TMR Associates, Inc
    Doing interesting things with small computers since 1979
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