On Wed, 11 Jan 2006, Chuck Ebbert wrote:
> In-Reply-To: <[email protected]>
>
> On Tue, 10 Jan 2006 at 22:07:44 +0100, Ingo Molnar wrote:
>
> > --- linux.orig/include/asm-i386/mutex.h
> > +++ linux/include/asm-i386/mutex.h
> > @@ -28,7 +28,13 @@ do { \
> > \
> > __asm__ __volatile__( \
> > LOCK " decl (%%eax) \n" \
> > - " js "#fail_fn" \n" \
> > + " js 2f \n" \
> > + "1: \n" \
> > + \
> > + LOCK_SECTION_START("") \
> > + "2: call "#fail_fn" \n" \
> > + " jmp 1b \n" \
> > + LOCK_SECTION_END \
> > \
> > :"=a" (dummy) \
> > : "a" (count) \
>
>
> But now it's inefficient again.
>
> Why not this:
>
> LOCK " decl (%%eax) \n" \
> " jns 1f \n" \
> " call "#fail_fn" \n" \
> "1: \n" \
> \
> :"=a" (dummy) \
> : "a" (count) \
>
>
> Will the extra taken forward conditional jump in the fastpath cause much
> of a slowdown?
yeah - the fastpath is much more common than the slowpath.
Ingo
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