perf_events: Add new start/stop PMU callbacks
In certain situations, the kernel may need to stop and start the same
event rapidly. The current PMU callbacks do not distinguish between stop
and release (i.e., stop + free the resource). Thus, a counter may be
released, then it will be immediately re-acquired. Event scheduling will
again take place with no guarantee to assign the same counter. On some
processors, this may event yield to failure to assign the event back due
to competion between cores.
This patch is adding a new pair of callback to stop and restart a counter
without actually release the underlying counter resource. On stop, the
counter is stopped, its values saved and that's it. On start, the value
is reloaded and counter is restarted (on x86, actual restart is delayed
until perf_enable()).
Signed-off-by: Stephane Eranian <eranian@google.com>
[ added fallback to ->enable/->disable for all other PMUs
fixed x86_pmu_start() to call x86_pmu.enable()
merged __x86_pmu_disable into x86_pmu_stop() ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4b703875.0a04d00a.7896.ffffb824@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index a920f17..9173ea9 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1495,7 +1495,7 @@
hwc->last_tag == cpuc->tags[i];
}
-static void __x86_pmu_disable(struct perf_event *event, struct cpu_hw_events *cpuc);
+static void x86_pmu_stop(struct perf_event *event);
void hw_perf_enable(void)
{
@@ -1533,7 +1533,7 @@
match_prev_assignment(hwc, cpuc, i))
continue;
- __x86_pmu_disable(event, cpuc);
+ x86_pmu_stop(event);
hwc->idx = -1;
}
@@ -1801,6 +1801,19 @@
return 0;
}
+static int x86_pmu_start(struct perf_event *event)
+{
+ struct hw_perf_event *hwc = &event->hw;
+
+ if (hwc->idx == -1)
+ return -EAGAIN;
+
+ x86_perf_event_set_period(event, hwc, hwc->idx);
+ x86_pmu.enable(hwc, hwc->idx);
+
+ return 0;
+}
+
static void x86_pmu_unthrottle(struct perf_event *event)
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
@@ -1924,8 +1937,9 @@
event->pending_kill = POLL_IN;
}
-static void __x86_pmu_disable(struct perf_event *event, struct cpu_hw_events *cpuc)
+static void x86_pmu_stop(struct perf_event *event)
{
+ struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
int idx = hwc->idx;
@@ -1954,7 +1968,7 @@
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
int i;
- __x86_pmu_disable(event, cpuc);
+ x86_pmu_stop(event);
for (i = 0; i < cpuc->n_events; i++) {
if (event == cpuc->event_list[i]) {
@@ -2667,6 +2681,8 @@
static const struct pmu pmu = {
.enable = x86_pmu_enable,
.disable = x86_pmu_disable,
+ .start = x86_pmu_start,
+ .stop = x86_pmu_stop,
.read = x86_pmu_read,
.unthrottle = x86_pmu_unthrottle,
};