From: Arjan Koers <0h61vkll2ly8@xutrox.com>
To: Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm@vger.kernel.org, Glauber Costa <glommer@redhat.com>
Subject: [PATCH] KVM: pvclock_clocksource_read while-loop optimization
Date: Sat, 01 Jan 2011 21:51:03 +0100 [thread overview]
Message-ID: <4D1F93B7.4080707@xutrox.com> (raw)
Reduce the number of while-loop iterations (from two to one in the most
common situation)
Signed-off-by: Arjan Koers <0h61vkll2ly8@xutrox.com>
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 42eb330..8f52acb 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -93,7 +93,7 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
struct pvclock_shadow_time shadow;
unsigned version;
cycle_t ret, offset;
- u64 last;
+ u64 last, save;
do {
version = pvclock_get_time_values(&shadow, src);
@@ -125,8 +125,9 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
do {
if (ret < last)
return last;
+ save = last;
last = atomic64_cmpxchg(&last_value, last, ret);
- } while (unlikely(last != ret));
+ } while (unlikely(last != save));
return ret;
}
next reply other threads:[~2011-01-01 20:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-01 20:51 Arjan Koers [this message]
2011-01-03 16:50 ` [PATCH] KVM: pvclock_clocksource_read while-loop optimization Glauber Costa
-- strict thread matches above, loose matches on Subject: below --
2010-10-19 20:05 Arjan Koers
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