On Tue, Aug 29, 2017 at 10:10:37PM +0200, Thomas Gleixner wrote:
> On Tue, 29 Aug 2017, Peter Zijlstra wrote:
> > So I have a patch _somewhere_ that preserves the event<->cpu relation
> > across hotplug and disable/enable would be sufficient. If you want I can
> > try and dig that out and make it work again.
> >
> > That would avoid having to do the destroy/create cycle of the watchdog
> > events.
>
> Yes, that would solve the x86_release_hw() issue, but still lots of the
> other rework is required in one way or the other.
>
> I'm currently trying to avoid that extra lock mess in the cpu hotplug code,
> which would just open the door for everybody to add his extra locks there,
> so we end up taking a gazillion locks before we can hotplug :)
>
> I think I have an idea how to solve that cleanly, but certainly your offer
> of preserving the event - cpu relation accross hotplug would help
> tremendously.
I think something like the below ought to work. Compile tested only.
On offline it basically does perf_event_disable() for all CPU context
events, and then adds HOTPLUG_OFFSET (-32) to arrive at: OFF +
HOTPLUG_OFFSET = -33.
That's smaller than ERROR and thus perf_event_enable() no-ops on events
for offline CPUs (maybe we should try and plumb an error return for
IOC_ENABLE).
On online we subtract the HOTPLUG_OFFSET again and the event becomes a
regular OFF, after which perf_event_enable() should work again.
---
include/linux/perf_event.h | 2 ++
kernel/events/core.c | 51 +++++++++++++++++++++++++++++++++-------------
2 files changed, 39 insertions(+), 14 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9bac4bfa5e1a..7b39ceeb206b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -497,6 +497,8 @@ enum perf_event_active_state {
PERF_EVENT_STATE_OFF = -1,
PERF_EVENT_STATE_INACTIVE = 0,
PERF_EVENT_STATE_ACTIVE = 1,
+
+ PERF_EVENT_STATE_HOTPLUG_OFFSET = -32,
};
struct file;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f77c97477e08..b277c27fd81e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11025,19 +11025,21 @@ void perf_swevent_init_cpu(unsigned int cpu)
}
#if defined CONFIG_HOTPLUG_CPU || defined CONFIG_KEXEC_CORE
-static void __perf_event_exit_context(void *__info)
+static void __perf_event_exit_cpu(void *__info)
{
- struct perf_event_context *ctx = __info;
- struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+ struct perf_cpu_context *cpuctx = __info;
+ struct perf_event_context *ctx = &cpuctx->ctx;
struct perf_event *event;
raw_spin_lock(&ctx->lock);
- list_for_each_entry(event, &ctx->event_list, event_entry)
- __perf_remove_from_context(event, cpuctx, ctx, (void
*)DETACH_GROUP);
+ list_for_each_entry(event, &ctx->event_list, event_entry) {
+ __perf_event_disable(event, cpuctx, ctx, NULL);
+ event->state += PERF_EVENT_STATE_HOTPLUG_OFFSET;
+ }
raw_spin_unlock(&ctx->lock);
}
-static void perf_event_exit_cpu_context(int cpu)
+int perf_event_exit_cpu(unsigned int cpu)
{
struct perf_cpu_context *cpuctx;
struct perf_event_context *ctx;
@@ -11049,17 +11051,43 @@ static void perf_event_exit_cpu_context(int cpu)
ctx = &cpuctx->ctx;
mutex_lock(&ctx->mutex);
- smp_call_function_single(cpu, __perf_event_exit_context, ctx,
1);
+ smp_call_function_single(cpu, __perf_event_exit_cpu, cpuctx, 1);
cpuctx->online = 0;
mutex_unlock(&ctx->mutex);
}
cpumask_clear_cpu(cpu, perf_online_mask);
mutex_unlock(&pmus_lock);
+
+ return 0;
+}
+
+static void __perf_event_init_cpu(void *__info)
+{
+ struct perf_cpu_context *cpuctx = __info;
+ struct perf_event_context *ctx = &cpuctx->ctx;
+ struct perf_event *event;
+
+ raw_spin_lock(&ctx->lock);
+ list_for_each_entry(event, &ctx->event_list, event_entry)
+ event->state -= PERF_EVENT_STATE_HOTPLUG_OFFSET;
+ raw_spin_unlock(&ctx->lock);
+}
+
+static void _perf_event_init_cpu(int cpu, struct perf_cpu_context *cpuctx)
+{
+ smp_call_function_single(cpu, __perf_event_init_cpu, cpuctx, 1);
}
+
#else
-static void perf_event_exit_cpu_context(int cpu) { }
+int perf_event_exit_cpu(unsigned int cpu)
+{
+ return 0;
+}
+static void _perf_event_init_cpu(int cpu, struct perf_cpu_context *cpuctx)
+{
+}
#endif
int perf_event_init_cpu(unsigned int cpu)
@@ -11078,6 +11106,7 @@ int perf_event_init_cpu(unsigned int cpu)
mutex_lock(&ctx->mutex);
cpuctx->online = 1;
+ _perf_event_init_cpu(cpu, cpuctx);
mutex_unlock(&ctx->mutex);
}
mutex_unlock(&pmus_lock);
@@ -11085,12 +11114,6 @@ int perf_event_init_cpu(unsigned int cpu)
return 0;
}
-int perf_event_exit_cpu(unsigned int cpu)
-{
- perf_event_exit_cpu_context(cpu);
- return 0;
-}
-
static int
perf_reboot(struct notifier_block *notifier, unsigned long val, void *v)
{
