linux-kernel - Re: [PATCH v3 3/3] perf tools: Enable on a list of CPUs for hybrid

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Message-ID: <57a972ea-bbe3-2baa-ab8d-9fbfe2eb4d32@linux.intel.com>
Date:   Fri, 23 Jul 2021 08:49:01 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v3 3/3] perf tools: Enable on a list of CPUs for hybrid

Hi Jiri,

On 7/22/2021 6:19 PM, Jiri Olsa wrote:
> On Wed, Jul 21, 2021 at 12:30:11PM +0800, Jin, Yao wrote:
>> Hi Jiri,
>>
>> On 7/20/2021 5:16 PM, Jiri Olsa wrote:
>>> On Tue, Jul 20, 2021 at 03:07:02PM +0800, Jin, Yao wrote:
>>>
>>> SNIP
>>>
>>>>
>>>> OK, evlist__fix_cpus() is better, use this name in v4.
>>>>
>>>>>> +{
>>>>>> +	struct perf_cpu_map *cpus;
>>>>>> +	struct evsel *evsel, *tmp;
>>>>>> +	struct perf_pmu *pmu;
>>>>>> +	int ret, unmatched_count = 0, events_nr = 0;
>>>>>> +
>>>>>> +	if (!perf_pmu__has_hybrid() || !cpu_list)
>>>>>> +		return 0;
>>>>>> +
>>>>>> +	cpus = perf_cpu_map__new(cpu_list);
>>>>>> +	if (!cpus)
>>>>>> +		return -1;
>>>>>> +
>>>>>> +	evlist__for_each_entry_safe(evlist, tmp, evsel) {
>>>>>> +		struct perf_cpu_map *matched_cpus, *unmatched_cpus;
>>>>>> +		char buf1[128], buf2[128];
>>>>>> +
>>>>>> +		pmu = perf_pmu__find_hybrid_pmu(evsel->pmu_name);
>>>>>> +		if (!pmu)
>>>>>> +			continue;
>>>>>> +
>>>>>> +		ret = perf_pmu__cpus_match(pmu, cpus, &matched_cpus,
>>>>>> +					   &unmatched_cpus);
>>>>>> +		if (ret)
>>>>>> +			goto out;
>>>>>> +
>>>>>> +		events_nr++;
>>>>>> +
>>>>>> +		if (matched_cpus->nr > 0 && (unmatched_cpus->nr > 0 ||
>>>>>> +		    matched_cpus->nr < cpus->nr ||
>>>>>> +		    matched_cpus->nr < pmu->cpus->nr)) {
>>>>>> +			perf_cpu_map__put(evsel->core.cpus);
>>>>>> +			perf_cpu_map__put(evsel->core.own_cpus);
>>>>>> +			evsel->core.cpus = perf_cpu_map__get(matched_cpus);
>>>>>> +			evsel->core.own_cpus = perf_cpu_map__get(matched_cpus);
>>>>>
>>>>> I'm bit confused in here.. AFAIUI there's 2 evsel objects create
>>>>> for hybrid 'cycles' ... should they have already proper cpus set?
>>>>>
>>>>
>>>> For 'cycles', yes two evsels are created automatically. One is for atom CPU
>>>> (e.g. 8-11), the other is for core CPU (e.g. 0-7). In this example, these 2
>>>> evsels have already the cpus set.
>>>
>>> hum, so those evsels are created with pmu's cpus, right?
>>>
>>
>> Yes, that's right. But we also check and adjust the evsel->cpus by using
>> user's cpu list on hybrid (what the evlist__use_cpu_list() does).
>>
>>>>
>>>> While the 'cpus' here is just the user specified cpu list.
>>>> cpus = perf_cpu_map__new(cpu_list);
>>>
>>> then I think they will be changed by evlist__create_maps
>>> with whatever user wants?
>>>
>>
>> No, it will not be changed by evlist__create_maps.
>>
>> In evlist__create_maps(),
>> evlist->core.has_user_cpus = !!target->cpu_list && !target->hybrid;
>>
>> It disables has_user_cpus for hybrid.
>>
>> So in __perf_evlist__propagate_maps, they will not be changed by evlist->cpus.
>>
>> if (!evsel->own_cpus || evlist->has_user_cpus) {
>> 	perf_cpu_map__put(evsel->cpus);
>> 	evsel->cpus = perf_cpu_map__get(evlist->cpus);
>> 	
>>> could we just change __perf_evlist__propagate_maps to follow
>>> pmu's cpus?
>>>
>>
>> In __perf_evlist__propagate_maps, it has already followed pmu's cpus because
>> the evlist->has_user_cpus is false for hybrid.
> 
> sorry for delay
> 

Never mind. :)

> ok, so we first fix the cpus on hybrid events and then
> propagate maps.. I guess it's ok, because it's in libperf
> and that has no notion of hybrid so far
> 

Yes. If we want the libperf to be hybrid aware, the interface has to be modified but actually we 
need to avoid modifying the libperf interface. So I finally decide to adjust the evsel->cpus first 
and then propatate maps.

> could you please rename that function so it's also obvious
> it's for hybrid only
> 
>    evlist__fix_hybrid_cpus ? not sure ;-)
> 

Sure, I will rename the funciton in v4.

> and add some comment with example to explain what the
> function is doing
> 

Got it!

Thanks
Jin Yao

> thanks,
> jirka
>