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    SubjectRe: [PATCH v4 0/3] random: convert to using iters, for Al Viro
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    On 5/20/22 9:39 AM, Jason A. Donenfeld wrote:
    > Hi Jens,
    >
    > On Fri, May 20, 2022 at 09:34:46AM -0600, Jens Axboe wrote:
    >> On 5/20/22 9:25 AM, Jason A. Donenfeld wrote:
    >>> Hi Jens,
    >>>
    >>> On Fri, May 20, 2022 at 11:44:56AM +0200, Jason A. Donenfeld wrote:
    >>>> Jens Axboe (3):
    >>>> random: convert to using fops->read_iter()
    >>>> random: convert to using fops->write_iter()
    >>>> random: wire up fops->splice_{read,write}_iter()
    >>>
    >>> FYI, this series makes reads from /dev/urandom slower, from around 616
    >>> MiB/s to 598 MiB/s on my system. That seems rather unfortunate.
    >>
    >> How reproducible is that? That seems like a huge difference for the
    >> change. How big are the reads?
    >
    > Fairly reproducible. Actually, if anything, it reproduces consistently
    > with worst results; I chose the most favorable ones for the new code.
    > This isn't any fancy `perf` profiling, but just running:
    >
    > $ pv /dev/urandom > /dev/null
    >
    > From looking at strace, the read size appears to be 131072.

    Ran 32, 1k, 4k here and it does seem to be down aboout 3%. Which is
    definitely bigger than I expected, particularly for larger reads. If
    anything, the 32b read seems comparably better than eg 1k or 4k, which
    is also unexpected. Let me do a bit of profiling to see what is up.

    If you're worried about it, I'd just keep the read/write and add the
    iter variants on the side.

    --
    Jens Axboe

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