glibc source rpm and nptl

[Jakub Jelinek]

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).

> make any difference [using athlon-mp and -O4].  Just seems odd not to 

Why specifically -O4?  -O3 or -O2147483647 do exactly the same.

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.

	Jakub