[Xen-devel] [PATCH] acpi: do not flush cache if cx->type != ACPI_STATE_C3

[Wei Wang <wei.wang2@xxxxxxx>]

Hi Jan,
This is a revised fix from my last post[1]. We found that the 
performance issue[2] is actually caused by an unnecessary cache flush 
when fall-through happens. According to acpi spec, c2 has cache 
consistency, we don't need cache flush if cx->type != ACPI_STATE_C3.
This fix improves performance of some OEM systems significantly. I would 
suggest to back port it to 4.1, 4.0 and even 3.4.
Thanks,
We

[1]
http://lists.xen.org/archives/html/xen-devel/2012-04/msg00395.html
[2]
http://forums.citrix.com/thread.jspa?threadID=297461&tstart=0&start=0

# HG changeset patch
# Parent 6efb9f934bfb4c46af375612fb01e65d15518380
# User Wei Wang <wei.wang2@xxxxxxx>
acpi: do not flush cache if cx->type != ACPI_STATE_C3

Signed-off-by: Wei Wang <wei.wang2@xxxxxxx>

diff -r 6efb9f934bfb -r 85775fd04cf4 xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c      Thu Apr 05 11:24:26 2012 +0100
+++ b/xen/arch/x86/acpi/cpu_idle.c      Thu Apr 12 14:15:09 2012 +0200
@@ -509,7 +509,8 @@ static void acpi_processor_idle(void)
         else if ( !power->flags.bm_check )
         {
             /* SMP with no shared cache... Invalidate cache  */
-            ACPI_FLUSH_CPU_CACHE();
+            if ( cx->type == ACPI_STATE_C3 )
+                ACPI_FLUSH_CPU_CACHE();
         }

         /* Invoke C3 */


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