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    SubjectRe: [PATCH 0/2] task_put batching
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    On 7/20/20 10:06 AM, Pavel Begunkov wrote:
    > On 20/07/2020 18:49, Jens Axboe wrote:
    >> On 7/20/20 9:22 AM, Pavel Begunkov wrote:
    >>> On 18/07/2020 17:37, Jens Axboe wrote:
    >>>> On 7/18/20 2:32 AM, Pavel Begunkov wrote:
    >>>>> For my a bit exaggerated test case perf continues to show high CPU
    >>>>> cosumption by io_dismantle(), and so calling it io_iopoll_complete().
    >>>>> Even though the patch doesn't yield throughput increase for my setup,
    >>>>> probably because the effect is hidden behind polling, but it definitely
    >>>>> improves relative percentage. And the difference should only grow with
    >>>>> increasing number of CPUs. Another reason to have this is that atomics
    >>>>> may affect other parallel tasks (e.g. which doesn't use io_uring)
    >>>>>
    >>>>> before:
    >>>>> io_iopoll_complete: 5.29%
    >>>>> io_dismantle_req: 2.16%
    >>>>>
    >>>>> after:
    >>>>> io_iopoll_complete: 3.39%
    >>>>> io_dismantle_req: 0.465%
    >>>>
    >>>> Still not seeing a win here, but it's clean and it _should_ work. For
    >>>> some reason I end up getting the offset in task ref put growing the
    >>>> fput_many(). Which doesn't (on the surface) make a lot of sense, but
    >>>> may just mean that we have some weird side effects.
    >>>
    >>> It grows because the patch is garbage, the second condition is always false.
    >>> See the diff. Could you please drop both patches?
    >>
    >> Hah, indeed. With this on top, it looks like it should in terms of
    >> performance and profiles.
    >
    > It just shows, that it doesn't really matters for a single-threaded app,
    > as expected. Worth to throw some contention though. I'll think about
    > finding some time to get/borrow a multi-threaded one.

    But it kind of did here, ended up being mostly a wash in terms of perf
    here as my testing reported. With the incremental applied, it's up a bit
    over before the task put batching.

    >> I can just fold this into the existing one, if you'd like.
    >
    > Would be nice. I'm going to double-check the counter and re-measure anyway.
    > BTW, how did you find it? A tool or a proc file would be awesome.

    For this kind of testing, I just use t/io_uring out of fio. It's probably
    the lowest overhead kind of tool:

    # sudo taskset -c 0 t/io_uring -b512 -p1 /dev/nvme2n1

    --
    Jens Axboe

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