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    SubjectRe: Linux 2.6.29
    Linus Torvalds wrote:
    > On Thu, 2 Apr 2009, Jeff Garzik wrote:
    >> The most interesting thing I found: the SSD does 80 MB/s for the first ~1 GB
    >> or so, then slows down dramatically. After ~2GB, it is down to 32 MB/s.
    >> After ~4GB, it reaches a steady speed around 23 MB/s.
    > Are you sure that isn't an effect of double and triple indirect blocks
    > etc? The metadata updates get more complex for the deeper indirect blocks.

    > Or just our page cache lookup? Maybe our radix tree thing hits something
    > stupid. Although it sure shouldn't be _that_ noticeable.

    Indirect block overhead increased as the file grew to 23 GB, I'm sure...

    I should probably re-test pre-creating the file, _then_ running
    overwrite.c. That would at least guarantee the filesystem isn't
    allocating new blocks and metadata.

    I was really surprised the performance was so high at first, then fell
    off so dramatically, on the SSD here.

    Unfortunately I cannot trash these blkdevs, so the raw blkdev numbers
    are not immediately measurable.

    >> There is a similar performance fall-off for the Seagate, but much less
    >> pronounced:
    >> After 1GB: 52 MB/s
    >> After 2GB: 44 MB/s
    >> After 3GB: steady state
    > That would seem to indicate that it's something else than the disk speed.
    >> There appears to be a small increase in system time with "-f" (use fadvise),
    >> but I'm guessing time(1) does not really give a good picture of overall system
    >> time used, when you include background VM activity.
    > It would also be good to just compare it to something like
    > time sh -c "dd + sync"

    I'll add that to the next run...


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