Re: [PATCH] perf: Rewrite core context handling

[Ravi Bangoria]

On 10-Oct-22 3:44 PM, Peter Zijlstra wrote:
> On Wed, Sep 07, 2022 at 04:58:49PM +0530, Ravi Bangoria wrote:
>>> -static void
>>> -ctx_flexible_sched_in(struct perf_event_context *ctx,
>>> -		      struct perf_cpu_context *cpuctx)
>>> +/* XXX .busy thingy from Peter's patch */
>>> +static void ctx_flexible_sched_in(struct perf_event_context *ctx, struct pmu *pmu)
>>
>> This one turned out to be very easy. Given that, we iterate over each
>> pmu, we can just return error if we fail to schedule any flexible event.
>> (It wouldn't be straight forward like this if we needed to implement
>> pmu=NULL optimization.)
>>
>> ---
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index e0232e0bb74e..923656af73fe 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -3751,6 +3751,7 @@ static int merge_sched_in(struct perf_event *event, void *data)
>>  			cpc = this_cpu_ptr(event->pmu_ctx->pmu->cpu_pmu_context);
>>  			perf_mux_hrtimer_restart(cpc);
>>  			group_update_userpage(event);
>> +			return -EBUSY;
>>  		}
>>  	}
>>  
> 
> I'm afraid this breaks things; consider:
> 
>   f79256532682 ("perf/core: fix userpage->time_enabled of inactive events")
> 
> I totally hate this -- because it means we *HAVE* to iterate the
> inactive events, but alas.

Sure. Will drop this.

Thanks,
Ravi