Re: [rfc patch] i386: don't save eflags on task switch

Andi Kleen
2006-11-04T01:36:28Z

On Saturday 04 November 2006 01:46, Linus Torvalds wrote:
>
> On Fri, 3 Nov 2006, Chuck Ebbert wrote:
> >
> > There is no real need to save eflags in switch_to(). Instead,
> > we can keep a constant value in the and always
> > restore that.
>
> I don't really see the point. The "pushfl" isn't the expensive part, and
> it gives sane and expected semantics.
>
> The "popfl" is the expensive part, and that's the thing that can't really
> even be removed.

Well it could -- i made an attempt at it recently. But it would add
a little code to the SYSENTER entry code (basically a test / conditional
jump after the pushfl there) to clear any rogue flags on entry.
Not sure it is worth it. That is why i didn't put this patch in.

-Andi