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SubjectRe: [RFC][PATCH] perf: Rewrite core context handling
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Hi,

On 17.10.2018 19:30, Peter Zijlstra wrote:
> On Wed, Oct 17, 2018 at 11:57:49AM +0300, Alexey Budankov wrote:
>> Hi,
>>
>> On 10.10.2018 13:45, Peter Zijlstra wrote:
>> <SNIP>
>>> -static bool perf_rotate_context(struct perf_cpu_context *cpuctx)
>>> +/*
>>> + * XXX somewhat completely buggered; this is in cpu_pmu_context, but we need
>>> + * event_pmu_context for rotations. We also need event_pmu_context specific
>>> + * scheduling routines. ARGH
>>> + *
>>> + * - fixed the cpu_pmu_context vs event_pmu_context thingy
>>> + * (cpu_pmu_context embeds an event_pmu_context)
>>> + *
>>> + * - need nr_events/nr_active in epc to do per epc rotation
>>> + * (done)
>>> + *
>>> + * - need cpu and task pmu ctx together...
>>> + * (cpc->task_epc)
>>> + */
>>> +static bool perf_rotate_context(struct perf_cpu_pmu_context *cpc)
>>
>> Since it reduces to single cpu context (and single task context) at all times,
>> ideally, it would probably be coded as simple as this:
>>
>> perf_rotate_context()
>> {
>> cpu = this_cpu_ptr(&cpu_context)
>> for_every_pmu(pmu, cpu)
>
> Can't do that, because we have per PMU rotation periods..

Well, yes, the callback is already called per-cpu per-pmu,
so then this simplifies a bit, like this:

perf_rotate_context(pmu, cpu)
{
for_every_event_ctx(event_ctx, pmu)
rotate(event_ctx, pmu)
}


event_ctx
|
v
pmu (struct perf_cpu_pmu_context) -> ctx__0 -> ctx__1
| |
v v
sched_out -> fgroup00 fgroup01 -> event001 -> event101 -> event201
| ^ | ^
v | v |
fgroup10 fgroup11
| | | |
v | v |
sched_in -> fgroup20 fgroup21

>
>> for_every_event_ctx(event_ctx, pmu)
>> rotate(event_ctx, pmu)
>> }
>
> I'm also not sure I get the rest that follows... you only have to rotate
> _one_ event per PMU.

Yes. One group per PMU. It could end up in several HW counters reprogramming.

Thanks,
Alexey

>
> I'll try and understand the rest of you email later; brain has checked
> out for the day.
>

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