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Subject[tip:perf/urgent] perf_event: Allocate children's perf_event_ctxp at the right time
Commit-ID:  b93f7978ad6b46133e9453b90ccc057dc2429e75
Gitweb: http://git.kernel.org/tip/b93f7978ad6b46133e9453b90ccc057dc2429e75
Author: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
AuthorDate: Wed, 9 Dec 2009 11:29:44 +0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Dec 2009 09:56:27 +0100

perf_event: Allocate children's perf_event_ctxp at the right time

In current code, children task will allocate memory for
'child->perf_event_ctxp' if the parent is counted, we can
do it only if the parent allowed children inherit it.

It can save memory and reduce overhead.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <4B1F19A8.5040805@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/perf_event.c | 37 ++++++++++++++++++++++---------------
1 files changed, 22 insertions(+), 15 deletions(-)
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 2b06c45..77641ae 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5083,7 +5083,7 @@ again:
*/
int perf_event_init_task(struct task_struct *child)
{
- struct perf_event_context *child_ctx, *parent_ctx;
+ struct perf_event_context *child_ctx = NULL, *parent_ctx;
struct perf_event_context *cloned_ctx;
struct perf_event *event;
struct task_struct *parent = current;
@@ -5099,20 +5099,6 @@ int perf_event_init_task(struct task_struct *child)
return 0;

/*
- * This is executed from the parent task context, so inherit
- * events that have been marked for cloning.
- * First allocate and initialize a context for the child.
- */
-
- child_ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
- if (!child_ctx)
- return -ENOMEM;
-
- __perf_event_init_context(child_ctx, child);
- child->perf_event_ctxp = child_ctx;
- get_task_struct(child);
-
- /*
* If the parent's context is a clone, pin it so it won't get
* swapped under us.
*/
@@ -5142,6 +5128,26 @@ int perf_event_init_task(struct task_struct *child)
continue;
}

+ if (!child->perf_event_ctxp) {
+ /*
+ * This is executed from the parent task context, so
+ * inherit events that have been marked for cloning.
+ * First allocate and initialize a context for the
+ * child.
+ */
+
+ child_ctx = kzalloc(sizeof(struct perf_event_context),
+ GFP_KERNEL);
+ if (!child_ctx) {
+ ret = -ENOMEM;
+ goto exit;
+ }
+
+ __perf_event_init_context(child_ctx, child);
+ child->perf_event_ctxp = child_ctx;
+ get_task_struct(child);
+ }
+
ret = inherit_group(event, parent, parent_ctx,
child, child_ctx);
if (ret) {
@@ -5170,6 +5176,7 @@ int perf_event_init_task(struct task_struct *child)
get_ctx(child_ctx->parent_ctx);
}

+exit:
mutex_unlock(&parent_ctx->mutex);

perf_unpin_context(parent_ctx);

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