[PATCH -mm] x86_64 apic.h cpu_relax() (was: [RFC -mm] more cpu_relax() places?)

[Andreas Mohr <andi@rhlx01.fht-esslingen.de>]

Hi all,

On Mon, Jun 12, 2006 at 08:37:43PM +0200, Andreas Mohr wrote:
> Hi all,
> 
> while reviewing 2.6.17-rc6-mm1, I found some places that might
> want to make use of cpu_relax() in order to not block secondary
> pipelines while busy-polling (probably especially useful on SMT CPUs):

Patch no. 3 of 3.

This one is adding a cpu_relax() that already existed in the i386 version.
Any reason this wasn't there, too?

Signed-off-by: Andreas Mohr <andi@lisas.de>


diff -urN linux-2.6.17-rc6-mm2.orig/include/asm-x86_64/apic.h linux-2.6.17-rc6-mm2.my/include/asm-x86_64/apic.h
--- linux-2.6.17-rc6-mm2.orig/include/asm-x86_64/apic.h	2006-06-13 19:28:16.000000000 +0200
+++ linux-2.6.17-rc6-mm2.my/include/asm-x86_64/apic.h	2006-06-13 19:34:08.000000000 +0200
@@ -49,7 +49,8 @@
 
 static __inline__ void apic_wait_icr_idle(void)
 {
-	while ( apic_read( APIC_ICR ) & APIC_ICR_BUSY );
+	while ( apic_read( APIC_ICR ) & APIC_ICR_BUSY )
+		cpu_relax();
 }
 
 static inline void ack_APIC_irq(void)