On Wed, Feb 06, 2002 at 02:13:45PM +0000, Alan Cox wrote:
> > glibc 2.3 seems to plan to use segment register based thread local data for
> > even non threaded programs, so it would be a good idea to optimize LDT
> > allocation a bit (= not allocate 64K of vmalloc space every time
> > sys_modify_ldt is called - there is only 8MB of it)
>
> I think it would be a good idea to modify the glibc authors in that case.
> The ldt costs real performance on task switches. It would be very dumb of
> glibc to use it except when justified in the bigger picture - ie threaded
> apps
Are you sure it does? LGDT with non zero argument shouldn't be that costly.
The %fs switching adds some locked cycles for reloading the segment cache,
but because Windows uses that I would it expect to be reasonably optimized
on CPUs.
I actually tried to complain because on x86-64 it is more costly, but to
no avail.
-Andi
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This archive was generated by hypermail 2b29 : Thu Feb 07 2002 - 21:00:49 EST