glibc source rpm and nptl

[Rakesh Patel]

Jakub Jelinek wrote:

>On Sun, Nov 30, 2003 at 03:41:39PM -0500, Rakesh Patel wrote:
>  
>
>>So the Fedora Core 1 Kernel for x86 uses NPTL but the glibc for x86 does 
>>not? 
>>    
>>
>
>If you install glibc-2.3.2*.i386.rpm, then it does not use NPTL.
>This is the library which should be installed on all < i686 CPUs
>(where i686 in this context means i686 CPUs with CMOV instructions).
>
>  
>

>But, on almost all current x86 boxes you want glibc-2.3.2*.i686.rpm
>installed (FC1 installer or up2date will certainly prefer this package if the
>hardware supports it) and that has NPTL support in it.
>Similarly it supports NPTL if you build a .athlon.rpm package (not included
>in the distribution, because the gains are not even measurable).
>  
>

Yes, my install was certainly the i686 version after checking.  
Obviously I misunderstood what was installed
on my machine.

>>make any difference [using athlon-mp and -O4].  Just seems odd not to 
>>    
>>
>
>Why specifically -O4?  -O3 or -O2147483647 do exactly the same.
>
>  
>
You can ignore that one - I know -O3 was the highest level supported by 
gcc a few years ago. I just used -O4 since I saw
references to it recently and assumed there may have been additional 
optimizations supported by gcc since
2.x.  

>Also, it would surprise me if you see a significant difference with
>-march=athlon-mp vs. -march=i686 compiled glibc.  Athlon's reorder the
>instructions themselves a lot and so are much less sensitive to instruction
>scheduling.  Using -mfpmath=sse for glibc is a bad idea, since it could
>make the math library less accurate (given the assumptions some routines
>do).  The most important instructions which actually matter for performance
>(CMOV*; worth on average something like 1%-2%) are already used by
>glibc-*.i686.rpm.  And there are no Athlon optimized assembly string
>operations in glibc.  This is something which would actually be worth
>doing, so if somebody is looking for a project he can try to do something
>and benchmark it.
>
>  
>
Well since I was mistaken on what levels of optmization were provided by 
default, I obviously was wasting effort
assuming it functioned similarly to previous Redhat releases.

>	Jakub
>
>
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>