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Re: Ping: [PATCH v4] faster strlen on x64
On Thu, Feb 28, 2013 at 04:14:47PM +0400, Dmitrieva Liubov wrote:
> Hi,
>
> I remember you checked at least previous version on Atom but just
> don't put it here
> http://kam.mff.cuni.cz/~ondra/benchmark_string/strlen_profile.html
> Right?
Yes, atom is a notebook which I need to borrow and I did not have it at
that time.
>
> --
> Liubov Dmitrieva
> Intel Corporation
>
> 2013/2/25 OndÅej BÃlka <neleai@seznam.cz>:
> > Ping,
> >
> >
> > On Wed, Feb 13, 2013 at 12:38:40PM +0100, OndÅej BÃlka wrote:
> >> Hello,
> >>
> >> I wrote at previous version that unaligned read of first 16 bytes is bad
> >> tradeoff. When I made faster strcpy header I realized that it was because
> >> I was doing separate check if it crosses page.
> >>
> >> When I do only check if next 64 bytes do not cross page and first do
> >> unaligned 16 byte load then it causes only small overhead for larger
> >> strings. This makes my implementation faster for wider family of
> >> workloads. It speed up gcc benchmark and most other programs.
> >>
> >> On unit tests revised version is somewhat slower than previous version.
> >> It is caused by choosing first 16 bytes only rarely which causes branch
> >> misprediction.
> >>
> >> I did two additional small improvements, first is squashing padding patch.
> >> Second bit is test to cross page can be done as x%4096 < 4096-48 instead
> >> x%4096 <= 4096-64 because I align x into 16 bytes.
> >>
> >> I updated benchmarks, difference between new and revised version is at
> >> http://kam.mff.cuni.cz/~ondra/benchmark_string/strlen_profile.html
> >> http://kam.mff.cuni.cz/~ondra/strlen_profile.tar.bz2
> >>
> >>
> >> Ondra
> >