>Den söndag, 15 mars 2015 20:13 skrev Pádraig Brady <p...@draigbrady.com>:
>
>
>>On 15/03/15 08:33, Kristoffer Brånemyr wrote:>>
>> Hi,
>>
>> I did some tests and found out you can actually beat memchr with a simple
>> loop. Tests were done on >>a Intel Xeon E3-1231v3 (4*3.4GHz), on a 4GB file
>> that was already cached in memory. >>Benchmarking >was done simply with the
>> 'time' command. I don't know how this code would run on >>other
>> >architectures, but I guess you could put it in an #ifdef?
>>
>> Coreutils 2.83 version, compiled with -O3:
>> 507755520 /home/ztion/words
>>
>> real 0m3.126s
>> user 0m2.699s
>> sys 0m0.429s
>>
>>
>> Improved version compiled with -O2:
>> 507755520 /home/ztion/words
>>
>> real 0m2.857s
>> user 0m2.461s
>> sys 0m0.396s
>>
>> Improved version compiled with -O3:
>> 507755520 /home/ztion/words
>>
>> real 0m1.518s
>> user 0m1.157s
>> sys 0m0.361s
>>
>> I studied the generated assembly and with -O3 gcc generates some fancy SSE
>> code, getting some nice speedups. memchr is also SSE optimized as far as I
>> know, so it's interesting that this is so much faster, twice as fast
>> actually.
>>
>> In case you don't like turning -O3 on for some reason (the default in
>> coreutils is -O2 i think), the best version I could put together for -O2 was
>> this:
>>
>> Improved version 2, compiled with -O2:
>> 507755520 /home/ztion/words
>>
>> real 0m2.206s
>> user 0m1.827s
>> sys 0m0.379s
>Interesting. Thanks for the results.
>I use 'gcc -march=native -g -O3' locally, and with that can't see a difference
>in performance.
>
>What version of glibc and gcc are you using?
>gcc-4.9.2-1.fc21.x86_64 and glibc-2.20-7.fc21.x86_64 here.
>
>thanks,
>Pádraig.
Hi,
This is with gcc 4.9.2-7 and glibc 2.19-17 on Debian amd64. The difference is
still there for me when compiling with your CFLAGS. Have they improved memchr
in glibc 2.20? I don't think they have that yet in debian unfortunately.
What cpu do you have? -- /Kristoffer Brånemyr
