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    SubjectRe: Lockless page cache test results
    On Wed, Apr 26 2006, Andrew Morton wrote:
    > Jens Axboe <axboe@suse.de> wrote:
    > >
    > > Running a splice benchmark on a 4-way IPF box, I decided to give the
    > > lockless page cache patches from Nick a spin. I've attached the results
    > > as a png, it pretty much speaks for itself.
    >
    > It does.
    >
    > What does the test do?
    >
    > In particular, does it cause the kernel to take tree_lock once per
    > page, or once per batch-of-pages?

    Once per page, it's basically exercising the generic_file_splice_read()
    path. Basically X number of "clients" open the same file, and fill those
    pages into a pipe using splice. The output end of the pipe is then
    spliced to /dev/null to toss it away again. The top of the 4-client
    vanilla run profile looks like this:

    samples % symbol name
    65328 47.8972 find_get_page

    Basically the machine is fully pegged, about 7% idle time.

    We can speedup the lookups with find_get_pages(). The test does 64k max,
    so with luck we should be able to pull 16 pages in at the time. I'll try
    and run such a test. But boy I wish find_get_pages_contig() was there
    for that. I think I'd prefer adding that instead of coding that logic in
    splice, it can get a little tricky.

    --
    Jens Axboe

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