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    SubjectRe: remove the last set_fs() in common code, and remove it for x86 and powerpc
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    Le 18/08/2020 à 20:05, Christoph Hellwig a écrit :
    > On Tue, Aug 18, 2020 at 07:46:22PM +0200, Christophe Leroy wrote:
    >> I gave it a go on my powerpc mpc832x. I tested it on top of my newest
    >> series that reworks the 32 bits signal handlers (see
    >> https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=196278) with
    >> the microbenchmark test used is that series.
    >>
    >> With KUAP activated, on top of signal32 rework, performance is boosted as
    >> system time for the microbenchmark goes from 1.73s down to 1.56s, that is
    >> 10% quicker
    >>
    >> Surprisingly, with the kernel as is today without my signal's series, your
    >> series degrades performance slightly (from 2.55s to 2.64s ie 3.5% slower).
    >>
    >>
    >> I also observe, in both cases, a degradation on
    >>
    >> dd if=/dev/zero of=/dev/null count=1M
    >>
    >> Without your series, it runs in 5.29 seconds.
    >> With your series, it runs in 5.82 seconds, that is 10% more time.
    >
    > That's pretty strage, I wonder if some kernel text cache line
    > effects come into play here?
    >
    > The kernel access side is only used in slow path code, so it should
    > not make a difference, and the uaccess code is simplified and should be
    > (marginally) faster.
    >
    > Btw, was this with the __{get,put}_user_allowed cockup that you noticed
    > fixed?
    >

    Yes it is with the __get_user_size() replaced by __get_user_size_allowed().

    Christophe

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