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    SubjectRe: Multi-file USB mass-storage copy from PC to Nokia N900 slow when using CFQ
    On Tue, Jan 05, 2010 at 10:07:22AM -0600, Paul Hartman wrote:
    > Hi,

    I'm going to CC Jens on this email as he's the block device maintainer
    and might be in the better position to comment on this.

    > Copying more than one file from my PC (kernel 2.6.32) to my Nokia N900
    > over USB mass storage mode is very slow when CFQ is the i/o scheduler.
    > The target uses vfat filesystem.
    >
    > I am using iotop to monitor the I/O in general, plus I performed the
    > following test. file1 and file2 are each 700M and both housed on a
    > ramdrive for this test. They were deleted from the destination between
    > runs.
    >
    > # one file at a time with sync in-between, fast speeds:
    > $ sync; time sh -c "cp file1 /mnt/usb; sync; cp file2 /mnt/usb; sync"
    >
    > real 1m25.697s
    > user 0m0.005s
    > sys 0m2.509s
    >
    > # copy two files in a row, then sync, speed is bad:
    > $ sync; time sh -c "cp file1 file2 /mnt/usb; sync"
    >
    > real 6m51.439s
    > user 0m0.007s
    > sys 0m2.615s
    >
    >
    > Using all I/O schedulers, the speed of the first test was the same. So
    > it's only related to writing more than 1 file to the N900. The timing
    > results for the second test ended up as such:
    >
    > cfq: 6m51.439s
    > noop: 3m0.733s
    > anticipatory: 1m44.348s
    > deadline: 1m36.804s
    >
    >
    > Also, in 2.6.31 the speed was four times slower, so the removal of old
    > pdflush code may have made a difference in this case. Copying 1
    > gigabyte takes about 1 minute at optimal speed, about 5 minutes using
    > CFQ in kernel 2.6.32, and took about 20 minutes using CFQ in kernel
    > 2.6.31.
    >
    > I thought you may be interested in case there's room to improve the
    > scheduler. If you want any other info let me know!
    >
    > Thanks
    > Paul
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