Define a new PERF_PMU_TXN_READ interface to read a group of counters
at once.
pmu->start_txn() // Initialize before first event
for each event in group
pmu->read(event); // Queue each event to be read
pmu->commit_txn() // Read/update all queued counters
Note that we use this interface with all PMUs. PMUs that implement this
interface use the ->read() operation to _queue_ the counters to be read
and use ->commit_txn() to actually read all the queued counters at once.
PMUs that don't implement PERF_PMU_TXN_READ ignore ->start_txn() and
->commit_txn() and continue to read counters one at a time.
Thanks to input from Peter Zijlstra.
Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
---
Changelog[v4]
[Peter Zijlstra] Add lockdep_assert_held() in perf_event_read_group().
Make sure the entire transaction happens on the same CPU.
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 38 +++++++++++++++++++++++++++++++-------
2 files changed, 32 insertions(+), 7 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 44bf05f..da307ad 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -169,6 +169,7 @@ struct perf_event;
#define PERF_EVENT_TXN 0x1
#define PERF_PMU_TXN_ADD 0x1 /* txn to add/schedule event on PMU */
+#define PERF_PMU_TXN_READ 0x2 /* txn to read event group from PMU */
/**
* pmu::capabilities flags
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 951d835..b5aa92c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3176,6 +3176,7 @@ void perf_event_exec(void)
struct perf_read_data {
struct perf_event *event;
+ bool group;
int ret;
};
@@ -3186,8 +3187,10 @@ static void __perf_event_read(void *info)
{
struct perf_read_data *data = info;
struct perf_event *event = data->event;
+ struct perf_event *sub;
struct perf_event_context *ctx = event->ctx;
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+ struct pmu *pmu = event->pmu;
/*
* If this is a task context, we need to check whether it is
@@ -3205,10 +3208,25 @@ static void __perf_event_read(void *info)
update_cgrp_time_from_event(event);
}
update_event_times(event);
- if (event->state == PERF_EVENT_STATE_ACTIVE)
- event->pmu->read(event);
+ if (event->state != PERF_EVENT_STATE_ACTIVE)
+ goto unlock;
+
+ if (!data->group) {
+ pmu->read(event);
+ goto unlock;
+ }
+
+ pmu->start_txn(pmu, PERF_PMU_TXN_READ);
- data->ret = 0;
+ pmu->read(event);
+ list_for_each_entry(sub, &event->sibling_list, group_entry) {
+ if (sub->state == PERF_EVENT_STATE_ACTIVE)
+ pmu->read(sub);
+ }
+
+ data->ret = pmu->commit_txn(pmu);
+
+unlock:
raw_spin_unlock(&ctx->lock);
}
@@ -3231,6 +3249,7 @@ static int perf_event_read(struct perf_event *event, bool
group)
if (event->state == PERF_EVENT_STATE_ACTIVE) {
struct perf_read_data data = {
.event = event,
+ .group = group,
.ret = 0,
};
@@ -3743,7 +3762,13 @@ static u64 perf_event_aggregate(struct perf_event
*event, u64 *enabled,
lockdep_assert_held(&event->child_mutex);
list_for_each_entry(child, &event->child_list, child_list) {
+#if 0
+ /*
+ * TODO: Do we need this read() for group events on PMUs that
+ * don't implement PERF_PMU_TXN_READ transactions?
+ */
(void)perf_event_read(child, false);
+#endif
total += perf_event_count(child);
*enabled += child->total_time_enabled;
*running += child->total_time_running;
@@ -3821,7 +3846,7 @@ static int perf_read_group(struct perf_event *event,
mutex_lock(&leader->child_mutex);
- ret = perf_event_read(leader);
+ ret = perf_event_read(leader, true);
if (ret) {
mutex_unlock(&leader->child_mutex);
return ret;
@@ -3850,12 +3875,11 @@ static int perf_read_group(struct perf_event *event,
list_for_each_entry(sub, &leader->sibling_list, group_entry) {
n = 0;
- mutex_lock(&leader->child_mutex);
+ mutex_lock(&sub->child_mutex);
- (void)perf_event_read(sub, false);
values[n++] = perf_event_aggregate(sub, &enabled, &running);
- mutex_unlock(&leader->child_mutex);
+ mutex_unlock(&sub->child_mutex);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(sub);
--
1.7.9.5
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