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authorGleb Natapov <gleb@redhat.com>2011-11-27 17:59:09 +0200
committerIngo Molnar <mingo@elte.hu>2011-12-06 08:34:02 +0100
commitb202952075f62603bea9bfb6ebc6b0420db11949 (patch)
tree9c8e0538b455e68b5c371caba5b1585ed0ef9d8a /include/linux/perf_event.h
parentb79387ef185af2323594920923cecba5753c3817 (diff)
perf, core: Rate limit perf_sched_events jump_label patching
jump_lable patching is very expensive operation that involves pausing all cpus. The patching of perf_sched_events jump_label is easily controllable from userspace by unprivileged user. When te user runs a loop like this: "while true; do perf stat -e cycles true; done" ... the performance of my test application that just increments a counter for one second drops by 4%. This is on a 16 cpu box with my test application using only one of them. An impact on a real server doing real work will be worse. Performance of KVM PMU drops nearly 50% due to jump_lable for "perf record" since KVM PMU implementation creates and destroys perf event frequently. This patch introduces a way to rate limit jump_label patching and uses it to fix the above problem. I believe that as jump_label use will spread the problem will become more common and thus solving it in a generic code is appropriate. Also fixing it in the perf code would result in moving jump_label accounting logic to perf code with all the ifdefs in case of JUMP_LABEL=n kernel. With this patch all details are nicely hidden inside jump_label code. Signed-off-by: Gleb Natapov <gleb@redhat.com> Acked-by: Jason Baron <jbaron@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/20111127155909.GO2557@redhat.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/perf_event.h')
-rw-r--r--include/linux/perf_event.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index cb44c9e75660..564769cdb473 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1064,12 +1064,12 @@ perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
}
}
-extern struct jump_label_key perf_sched_events;
+extern struct jump_label_key_deferred perf_sched_events;
static inline void perf_event_task_sched_in(struct task_struct *prev,
struct task_struct *task)
{
- if (static_branch(&perf_sched_events))
+ if (static_branch(&perf_sched_events.key))
__perf_event_task_sched_in(prev, task);
}
@@ -1078,7 +1078,7 @@ static inline void perf_event_task_sched_out(struct task_struct *prev,
{
perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, NULL, 0);
- if (static_branch(&perf_sched_events))
+ if (static_branch(&perf_sched_events.key))
__perf_event_task_sched_out(prev, next);
}