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    SubjectRe: Linux 2.6.29
    Trenton D. Adams wrote:
    > On Thu, Apr 2, 2009 at 8:01 PM, Jeff Garzik <jeff@garzik.org> wrote:
    >> Linus Torvalds 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.
    >
    > Isn't that the kernel IO queue, and the dd averaging of transfer
    > speed? For example, once you hit the dirty ratio limit, that is when
    > it starts writing to disk. So, the first bit you'll see really fast
    > speeds, as it goes to memory, but it averages out over time to a
    > slower speed. As an example...

    overwrite.c is a special program that does this, in a loop:

    write(buffer-N) data to pagecache
    start buffer-N write-out to storage
    wait for buffer-(N-1) write-out to complete

    It uses the sync_file_range() system call, which is like fsync() on
    steroids, wearing cool sunglasses.

    Regards,

    Jeff






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