This is the mail archive of the mailing list for the glibc project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Proposal to handle __strstr_sse42 and friends issue on x86

On Wed, Dec 11, 2013 at 10:55:01AM +1000, Allan McRae wrote:
> Hi all,
> For those who need some background, see [1].  In short, there is an
> issue with __strstr_sse42 on x86 which has a variety of workarounds.
> Some distributions re-add the inline statement, which is clearly fragile
> and not a fix. Others remove the sse42 string functions - see [2].
> I am going to propose we adopt the removal of the SSE42 routines.  We
> can not ensure that binaries are built with a new enough compiler (gcc
> after 2000) and keep backwards compatibility.  Also, ensuring the stack
> is aligned when entering these functions would be a performance hit that
> would likely remove any advantage of the sse42 routine (not tested...),
> and there are proposals to remove the sse42 routines for both x86 and
> x86_64 due to quadratic complexity anyway [3,4].
> So applying the patch in [2] seems the best approach to me?  Any
> comments/objections?
I send a patch that improves strstr performance. It got acked by Liubov
Dmitrieva and I asked if there are more comments and forgoten about it.

I applied that now, 
sse42 routines are quite ineffective in that regard, with plain sse2 you
can get around five times faster. I planned to add a version that avoids
unaligned loads for older processors.

You can also use this one you just improve performance 15 times instead
30 if you expanded unaligned loads into aligned ones.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]