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SubjectRe: Timing performance regression 4.15 to 4.16-rc1
On Sun, Mar 11, 2018 at 02:02:03PM +0100, Zdenek Kabelac wrote:
> Hi
>
> I've noticed quite some drop of performance (around 15% in some cases) where
> execution of lvm2 tests took longer time - and while tests itself should not
> really load CPU system - the overall running time just got bigger.
>
> Running bisect game pointed clearly to this commit:
>
> ---
>
> commit 44c02a2c3dc55835e9f0d8ef73966406cd805001
> Author: Al Viro <viro@zeniv.linux.org.uk>
> Date: Thu Oct 5 12:59:44 2017 -0400
>
> dev_ioctl(): move copyin/copyout to callers
>
>
> ---
>
> clear revert of this commit on top of 3266b5bd97eaa72793df0b6e5a106c69ccc166c4
> (recent ~4.16-rc4) restored timing of tests back.
>
>
> I'm not sure why - so at this moment this is just a patch causing 15% longer
> running times on lvm2 test suite.

I find it very hard to believe, TBH. It doesn't go anywhere near drivers/md;
could you profile the damn thing and see where does it spend that extra time?

It really doesn't touch anything on non-sockets...

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