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Re: [PATCH 2/2][BZ #16640] Remove strtok assembly implementation.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: libc-alpha at sourceware dot org
- Date: Thu, 13 Mar 2014 02:20:11 -0400
- 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> <20140310212923 dot GG6407 at domone dot podge>
On 03/10/2014 05:29 PM, OndÅej BÃlka wrote:
> 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.
Are you saying then that the resulting code generated with gcc 4.4
is approximately the same performance as that generated with a
newer gcc, both of which are 2-4x faster than the assembly
implementation?
If that's the case then please commit your patch.
Cheers,
Carlos.