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tracing: optimize global_trace_clock cachelines

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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>
This commit is contained in:
Steven Rostedt 2009-09-15 12:24:22 -04:00 committed by Steven Rostedt
parent 555f386c98
commit 6ca6cca31d
1 changed files with 14 additions and 10 deletions
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24
kernel/trace/trace_clock.c
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@ -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);