tracing: optimize global_trace_clock cachelines
The prev_trace_clock_time is only read or written to when the
trace_clock_lock is taken. For better perfomance, they
should share the same cache line.
Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index b588fd8..20c5f92 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -66,10 +66,14 @@
* Used by plugins that need globally coherent timestamps.
*/
-static u64 prev_trace_clock_time;
-
-static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp =
- (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+/* keep prev_time and lock in the same cacheline. */
+static struct {
+ u64 prev_time;
+ raw_spinlock_t lock;
+} trace_clock_struct ____cacheline_aligned_in_smp =
+ {
+ .lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED,
+ };
u64 notrace trace_clock_global(void)
{
@@ -88,19 +92,19 @@
if (unlikely(in_nmi()))
goto out;
- __raw_spin_lock(&trace_clock_lock);
+ __raw_spin_lock(&trace_clock_struct.lock);
/*
* TODO: if this happens often then maybe we should reset
- * my_scd->clock to prev_trace_clock_time+1, to make sure
+ * my_scd->clock to prev_time+1, to make sure
* we start ticking with the local clock from now on?
*/
- if ((s64)(now - prev_trace_clock_time) < 0)
- now = prev_trace_clock_time + 1;
+ if ((s64)(now - trace_clock_struct.prev_time) < 0)
+ now = trace_clock_struct.prev_time + 1;
- prev_trace_clock_time = now;
+ trace_clock_struct.prev_time = now;
- __raw_spin_unlock(&trace_clock_lock);
+ __raw_spin_unlock(&trace_clock_struct.lock);
out:
raw_local_irq_restore(flags);