> > i thought task switch using tss was rather slower.  have you measured?
> 
> Btw, if we want to speed up the syscall path, we should be using sysenter/
> sysret on P4s. This is actually most efficiently supported with a
> per-CPU TSS. Otherwise, you need to do a wrmsr for each context
> switch, and wrmsr is very slow.

why do you think wrmsr is needed?
even with per-cpu TSS, all you need is copying esp into
somewhere pointed by SYSENTER_ESP, isn't it?

YAMAMOTO Takashi