Commit-ID: 1dcaac1ce07db672e2cb5b4ef9642990689bb2a1
Gitweb: http://git.kernel.org/tip/1dcaac1ce07db672e2cb5b4ef9642990689bb2a1
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 8 Mar 2016 17:56:05 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 21 Mar 2016 09:35:29 +0100
perf/core: Document some hotplug bits
Document some of the hotplug notifier usage.
Requested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/events/core.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 43e35fa..de24fbc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9449,10 +9449,29 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
+ /*
+ * This must be done before the CPU comes alive, because the
+ * moment we can run tasks we can encounter (software) events.
+ *
+ * Specifically, someone can have inherited events on kthreadd
+ * or a pre-existing worker thread that gets re-bound.
+ */
perf_event_init_cpu(cpu);
break;
case CPU_DOWN_PREPARE:
+ /*
+ * This must be done before the CPU dies because after that an
+ * active event might want to IPI the CPU and that'll not work
+ * so great for dead CPUs.
+ *
+ * XXX smp_call_function_single() return -ENXIO without a warn
+ * so we could possibly deal with this.
+ *
+ * This is safe against new events arriving because
+ * sys_perf_event_open() serializes against hotplug using
+ * get_online_cpus().
+ */
perf_event_exit_cpu(cpu);
break;
default:
--
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