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Re: [PATCH 2/2][BZ #16640] Remove strtok assembly implementation.
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Carlos O'Donell <carlos at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Mon, 10 Mar 2014 22:29:23 +0100
- Subject: Re: [PATCH 2/2][BZ #16640] Remove strtok assembly implementation.
- Authentication-results: sourceware.org; auth=none
- References: <20140227123238 dot GA26291 at domone dot podge> <20140227124206 dot GA26474 at domone dot podge> <5318A03D dot 3000705 at redhat dot com> <20140306163241 dot GA11843 at domone dot podge> <5318B58B dot 5040704 at redhat dot com> <20140306205212 dot GB11843 at domone dot podge> <53192422 dot 2050101 at redhat dot com>
On Thu, Mar 06, 2014 at 08:42:58PM -0500, Carlos O'Donell wrote:
> On 03/06/2014 03:52 PM, OndÅej BÃlka wrote:
> > On Thu, Mar 06, 2014 at 12:51:07PM -0500, Carlos O'Donell wrote:
> >> On 03/06/2014 11:32 AM, OndÅej BÃlka wrote:
> >>> On Thu, Mar 06, 2014 at 11:20:13AM -0500, Carlos O'Donell wrote:
> >>>> On 02/27/2014 07:42 AM, OndÅej BÃlka wrote:
> >>>>> As followup this patch removes strtok assembly implementation as it is
> >>>>> around 2-4 times slower on sse4_2 capable machines which is a majority,
> >>>>> as previous benchtest demonstrated.
> >>>>>
> >>>>> You could try to gain some cycles on older machines by using ifuncs but
> >>>>> is a strtok important enough to complicate matters?
> >>>>>
> >>>>> OK to commit?
> >>>>>
> >>>>> * sysdeps/i386/i686/strtok.S: Remove.
> >>>>> * sysdeps/i386/i686/strtok_r.S: Likewise.
> >>>>> * sysdeps/i386/strtok.S: Likewise.
> >>>>> * sysdeps/i386/strtok_r.S: Likewise.
> >>>>> * sysdeps/x86_64/strtok.S: Likewise.
> >>>>> * sysdeps/x86_64/strtok_r.S: Likewise.
> >>>>
> >>>> Is this still the case with the oldest compiler we support?
> >>>>
> >>> I do not understand what are you reffering to.
> >>
> >> If you remove the strtok assembly implemetnation, the build will
> >> fall back on use the C implementation e.g. string/strtok.c.
> >> That C implementation will have been compiled by whichever
> >> compiler you're using for your build. In glibc we support a wide
> >> range of compilers from gcc 4.4 and newer. Do the older compilers,
> >> specifically gcc 4.4, still generate good code for strtok.c which
> >> is faster than strtok.S?
> >>
> > There is nothing to optimize, strtok code consist from two function
> > calls and some ifs and I do not see optimization oppurtinities here.
> >
>
> The problem I'm seeing is that we are removing assembly versions
> which might be faster than the code generated by the oldest and
> possible worst performing compiler that we support (assuming that
> gcc gets better with each revision).
>
> Could you please test with gcc 4.4 and see if it still generates
> 2-4x faster strtok or if the assembly version is faster?
>
When I tested this I found no difference in compilers but found that
speedup was caused by inlining. There is little difference on
implementations when I do not inline it.