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Subject[[PATCH v6 03/10] perf: Split perf_event_read() and perf_event_count()
Date
perf_event_read() does two things:

- call the PMU to read/update the counter value, and
- compute the total count of the event and its children

Not all callers need both. perf_event_reset() for instance needs the
first piece but doesn't need the second. Similarly, when we implement
the ability to read a group of events using the transaction interface,
we would need the two pieces done independently.

Break up perf_event_read() and have it just read/update the counter
and have the callers compute the total count if necessary.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
kernel/events/core.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e221432..01ede6b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3275,7 +3275,7 @@ u64 perf_event_read_local(struct perf_event *event)
return val;
}

-static u64 perf_event_read(struct perf_event *event)
+static void perf_event_read(struct perf_event *event)
{
/*
* If event is enabled and currently active on a CPU, update the
@@ -3301,8 +3301,6 @@ static u64 perf_event_read(struct perf_event *event)
update_event_times(event);
raw_spin_unlock_irqrestore(&ctx->lock, flags);
}
-
- return perf_event_count(event);
}

/*
@@ -3818,14 +3816,18 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
*running = 0;

mutex_lock(&event->child_mutex);
- total += perf_event_read(event);
+
+ perf_event_read(event);
+ total += perf_event_count(event);
+
*enabled += event->total_time_enabled +
atomic64_read(&event->child_total_time_enabled);
*running += event->total_time_running +
atomic64_read(&event->child_total_time_running);

list_for_each_entry(child, &event->child_list, child_list) {
- total += perf_event_read(child);
+ perf_event_read(child);
+ total += perf_event_count(child);
*enabled += child->total_time_enabled;
*running += child->total_time_running;
}
@@ -3985,7 +3987,7 @@ static unsigned int perf_poll(struct file *file, poll_table *wait)

static void _perf_event_reset(struct perf_event *event)
{
- (void)perf_event_read(event);
+ perf_event_read(event);
local64_set(&event->count, 0);
perf_event_update_userpage(event);
}
--
1.7.9.5


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