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Subject[[PATCH v6 06/10] perf: Invert perf_read_group() loops
Date
From: Peter Zijlstra <peterz@infradead.org>

In order to enable the use of perf_event_read(.group = true), we need
to invert the sibling-child loop nesting of perf_read_group().

Currently we iterate the child list for each sibling, this precludes
using group reads. Flip things around so we iterate each group for
each child.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
Changes to Peter's patch:
- Add GFP_KERNEL to kzalloc().
- Pass in address of counter to atomic_read().
- Return event->size rather than leader->size (perf_read_group())
- Keep chkpatch happy.
---
kernel/events/core.c | 85 ++++++++++++++++++++++++++++++++------------------
1 file changed, 55 insertions(+), 30 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7bb9141..2c38c09 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3862,50 +3862,75 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
}
EXPORT_SYMBOL_GPL(perf_event_read_value);

-static int perf_read_group(struct perf_event *event,
- u64 read_format, char __user *buf)
+static void __perf_read_group_add(struct perf_event *leader,
+ u64 read_format, u64 *values)
{
- struct perf_event *leader = event->group_leader, *sub;
- struct perf_event_context *ctx = leader->ctx;
- int n = 0, size = 0, ret;
- u64 count, enabled, running;
- u64 values[5];
+ struct perf_event *sub;
+ int n = 1; /* skip @nr */

- lockdep_assert_held(&ctx->mutex);
+ perf_event_read(leader, true);
+
+ /*
+ * Since we co-schedule groups, {enabled,running} times of siblings
+ * will be identical to those of the leader, so we only publish one
+ * set.
+ */
+ if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) {
+ values[n++] += leader->total_time_enabled +
+ atomic64_read(&leader->child_total_time_enabled);
+ }

- count = perf_event_read_value(leader, &enabled, &running);
+ if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING) {
+ values[n++] += leader->total_time_running +
+ atomic64_read(&leader->child_total_time_running);
+ }

- values[n++] = 1 + leader->nr_siblings;
- if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
- values[n++] = enabled;
- if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
- values[n++] = running;
- values[n++] = count;
+ /*
+ * Write {count,id} tuples for every sibling.
+ */
+ values[n++] += perf_event_count(leader);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(leader);

- size = n * sizeof(u64);
+ list_for_each_entry(sub, &leader->sibling_list, group_entry) {
+ values[n++] += perf_event_count(sub);
+ if (read_format & PERF_FORMAT_ID)
+ values[n++] = primary_event_id(sub);
+ }
+}

- if (copy_to_user(buf, values, size))
- return -EFAULT;
+static int perf_read_group(struct perf_event *event,
+ u64 read_format, char __user *buf)
+{
+ struct perf_event *leader = event->group_leader, *child;
+ struct perf_event_context *ctx = leader->ctx;
+ int ret = event->read_size;
+ u64 *values;

- ret = size;
+ lockdep_assert_held(&ctx->mutex);

- list_for_each_entry(sub, &leader->sibling_list, group_entry) {
- n = 0;
+ values = kzalloc(event->read_size, GFP_KERNEL);
+ if (!values)
+ return -ENOMEM;

- values[n++] = perf_event_read_value(sub, &enabled, &running);
- if (read_format & PERF_FORMAT_ID)
- values[n++] = primary_event_id(sub);
+ values[0] = 1 + leader->nr_siblings;
+
+ /*
+ * By locking the child_mutex of the leader we effectively
+ * lock the child list of all siblings.. XXX explain how.
+ */
+ mutex_lock(&leader->child_mutex);

- size = n * sizeof(u64);
+ __perf_read_group_add(leader, read_format, values);
+ list_for_each_entry(child, &leader->child_list, child_list)
+ __perf_read_group_add(child, read_format, values);

- if (copy_to_user(buf + ret, values, size)) {
- return -EFAULT;
- }
+ mutex_unlock(&leader->child_mutex);

- ret += size;
- }
+ if (copy_to_user(buf, values, event->read_size))
+ ret = -EFAULT;
+
+ kfree(values);

return ret;
}
--
1.7.9.5


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