Re: [patch] [sched] x86 idle thread should clear %fs, %gs

[Ingo Molnar]

On Tue, 29 Jan 2002, Pavel Machek wrote:

> > so it appears that this lowlevel x86 performance bug(?) is more than 11
> > years old! :-)
>
> Probably 386's were not optimized for %fs==%gs==0 case?
>
> BTW does it really make a difference for the CPU?

whether %fs/%gs is 0 or not? With the current 2.5.3-pre6 task switching
code there definitely is a performance difference, because we optimize the
'both values are 0' case. With the original TSS-based task switching
microcode i suspect it made a difference as well. (switching between two
different %fs/%gs values should be slower.)

	Ingo