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    SubjectRe: SATA Performance with Intel ICH6
    On Fri, 24 Nov 2006 15:10:11 +0100
    "Martin A. Fink" <fink@mpe.mpg.de> wrote:

    > Here some measurement results:
    >
    > time dd if=/dev/zero of=test.zero bs=1M count=1000
    > results in
    >
    > real 0m52.561s
    > user 0m0.003s
    > sys 0m7.407s
    >
    > and strace dd... gives among other information
    > 6.84s 1004calls syscall: write
    >
    > So I spend 45s of 52s within the kernel. Why so long?

    Profiling the kernel will tell. Preferably with oprofile, but if for some
    reason that doesn't work, with the old profiler.

    I use this:

    #!/bin/sh
    sudo opcontrol --stop
    sudo opcontrol --shutdown
    sudo rm -rf /var/lib/oprofile
    sudo opcontrol --vmlinux=/boot/vmlinux-$(uname -r)
    sudo opcontrol --start-daemon
    sudo opcontrol --start
    time $@
    sudo opcontrol --stop
    sudo opcontrol --shutdown
    sudo opreport -l /boot/vmlinux-$(uname -r) | head -50

    I have seen PIO and MMIO operations on PCI busses take tremendous amounts
    of time when that bus is saturated with DMA transfers. But that was back
    in the old days.
    -
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