Alexander Shishkin <[email protected]> writes:
> Peter Zijlstra <[email protected]> writes:
>
>> On Wed, Jan 14, 2015 at 02:18:21PM +0200, Alexander Shishkin wrote:
>>> +static __init int pt_init(void)
>>> +{
>>
>>> + pt_pmu.pmu.attr_groups = pt_attr_groups;
>>> + pt_pmu.pmu.task_ctx_nr = perf_hw_context;
>>
>> I just noticed this one, how can this ever work? We want the PT thing to
>> always get programmed, right? -- because we disallow creating more than
>> 1?
>>
>> Which reminds me; does that exclusive thing you did not allow you to
>> create one cpu wide and one per task (they're separate contexts) events?
>> At which point we're not schedulable at all.
>>
>> By sticking it on the HW context list it can end up not being programed
>> because its stuck after a bunch of hardware events that don't all fit on
>> the PMU.
>>
>> Would not the SW list be more appropriate; the SW list is a list of
>> events that's guaranteed to be schedulable.
>
> You're right, of course.
>
> As for the exclusive events, how about something like the code below (on
> top of the previous exclusive event patch)? The only remaining issue
> that I see is creating cpu-wide events in the presence of per-thread
> (event->cpu==-1) events. Both would still work, but only one of them
> will actually get scheduled at a time. I'm thinking about adding a
> counter for per-thread events to struct pmu for this purpose, so that if
> any are present, we can disallow creating cpu-wide events. Or, we can
> leave it as it is.
>
> What do you think?
>
> ---
> kernel/events/core.c | 52
> +++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 47 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index cf0bf99f53..e8c86530e2 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7688,14 +7688,11 @@ static bool exclusive_event_match(struct perf_event
> *e1, struct perf_event *e2)
> return false;
> }
>
> -static bool exclusive_event_ok(struct perf_event *event,
> - struct perf_event_context *ctx)
> +static bool __exclusive_event_ok(struct perf_event *event,
> + struct perf_event_context *ctx)
> {
> struct perf_event *iter_event;
>
> - if (!(event->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
> - return true;
> -
> list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
> if (exclusive_event_match(iter_event, event))
> return false;
> @@ -7704,6 +7701,51 @@ static bool exclusive_event_ok(struct perf_event
> *event,
> return true;
> }
>
> +static bool __exclusive_event_ok_on_cpu(struct perf_event *event, int cpu)
> +{
> + struct perf_event_context *cpuctx;
> + bool ret;
> +
> + cpuctx = find_get_context(event->pmu, NULL, cpu);
> + mutex_lock(&cpuctx->mutex);
> + ret = __exclusive_event_ok(event, cpuctx);
> + perf_unpin_context(cpuctx);
> + put_ctx(cpuctx);
> + mutex_unlock(&cpuctx->mutex);
Actually, find_get_context() is not needed here, the following should be
sufficient:
cpuctx = &per_cpu_ptr(event->pmu->pmu_cpu_context, cpu)->ctx;
mutex_lock(&cpuctx->mutex);
ret = __exclusive_event_ok(event, cpuctx);
mutex_unlock(&cpuctx->mutex);
Regards,
--
Alex
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