x86_64: speedup touch_nmi_watchdog

Avoid dirtying remote cpu's memory if it already has the correct value.

Cc: Andi Kleen <ak@suse.de>
Cc: Konrad Rzeszutek <konrad@darnok.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/x86_64/kernel/nmi.c b/arch/x86_64/kernel/nmi.c
index 931c64bad5e6..edbbc59b7523 100644
--- a/arch/x86_64/kernel/nmi.c
+++ b/arch/x86_64/kernel/nmi.c
@@ -296,7 +296,7 @@ static DEFINE_PER_CPU(unsigned, last_irq_sum);
 static DEFINE_PER_CPU(local_t, alert_counter);
 static DEFINE_PER_CPU(int, nmi_touch);
 
-void touch_nmi_watchdog (void)
+void touch_nmi_watchdog(void)
 {
         if (nmi_watchdog > 0) {
                 unsigned cpu;
@@ -306,8 +306,10 @@ void touch_nmi_watchdog (void)
                  * do it ourselves because the alert count increase is not
                  * atomic.
                  */
-                for_each_present_cpu (cpu)
-                        per_cpu(nmi_touch, cpu) = 1;
+                for_each_present_cpu(cpu) {
+                        if (per_cpu(nmi_touch, cpu) != 1)
+                                per_cpu(nmi_touch, cpu) = 1;
+                }
         }
 
         touch_softlockup_watchdog();