Re: [PATCH] Speedup SMP kernel on UP box

[Daniel Jacobowitz]

On Sat, Mar 16, 2002 at 03:37:26PM -0800, Paul Menage wrote:
> In article <[e-mail]>,
> you write:
> >@@ -9,9 +9,15 @@
> >  */
> > 
> > #ifdef CONFIG_SMP
> >-#define LOCK "lock ; "
> >+#define LOCK "\n1:\tlock ; "
> >+#define LOCK_ADDR	"\n" \
> >+			".section .lock.init,\"a\"\n\t" \
> >+			".align 4\n\t" \
> >+			".long 1b\n" \
> >+			".previous\n"
> 
> 
> Why not do:
> 
> #define LOCK "1: lock ; \n" \
> 	 	".section .lock.init,\"a\"\n" \
> 		".align 4\n"\
> 		".long 1b\n"\
> 		".previous\n" 
> 
> Then you don't need the LOCK_ADDR macro, so most of atomic.h can be
> left as is. The assembler doesn't seem to care that there's a section
> change between the lock prefix and the instruction that it's locking.

Local labels work forwards as well as backwards:

 #define LOCK 
 	 	".section .lock.init,\"a\"\n" \
 		".align 4\n"\
 		".long 1f\n"\
 		".previous\n" 
		"1: lock ; \n"

I recommend not using "1" for your label, though, because probably
other bits of code that use locks have local loops in them.  It's to be
expected... just pick a less common number.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer