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Commit 6ca6cca3 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 555f386c

kernel/trace/trace_clock.c

+14 −10
Original line number Diff line number Diff line
@@ -66,10 +66,14 @@ u64 notrace trace_clock(void) 
 * 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 @@ u64 notrace trace_clock_global(void) 
	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);