linux-kernel - Re: [PATCH v3 12/27] perf parse-events: Support no alias assigned event inside hybrid PMU

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Date:   Fri, 16 Apr 2021 09:57:49 +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 12/27] perf parse-events: Support no alias assigned
 event inside hybrid PMU

Hi Jiri,

On 4/16/2021 3:39 AM, Jiri Olsa wrote:
> On Thu, Apr 15, 2021 at 10:53:33PM +0800, Jin, Yao wrote:
> 
> SNIP
> 
>>
>> With my current code,
>>
>> static int parse_events__with_hybrid_pmu(struct parse_events_state *parse_state,
>> 					 const char *str, char *pmu_name,
>> 					 struct list_head *list)
>> {
>> 	struct parse_events_state ps = {
>> 		.list           = LIST_HEAD_INIT(ps.list),
>> 		.stoken         = PE_START_EVENTS,
>> 		.pmu_name       = pmu_name,
>> 		.idx            = parse_state->idx,
>> 	};
>> 	int ret;
>>
>> 	ret = parse_events__scanner(str, &ps);
>> 	perf_pmu__parse_cleanup();
>>
>> 	if (!ret) {
>> 		if (!list_empty(&ps.list)) {
>> 			list_splice(&ps.list, list);
>> 			parse_state->idx = ps.idx;
>> 		}
>> 	}
>>
>> 	return ret;
>> }
>>
>> The new created evsels are added to the tail of list (ps.list) and ps.list
>> is joined to the list (the parameter 'list').
>>
>> If we want to reuse the __parse_events(), we may need to:
>>
>> struct evlist *evlist = evlist__new();
> 
> there's the original evlist pointer passed to the initial parser
> that we should use no?
>

Unfortunately the answer is no. :(

For "cpu_core/LLC-loads/", if we do the parser twice by just calling __parse_events, actually the 
__parse_events will be called two times.

int __parse_events(struct evlist *evlist, const char *str,
		   struct parse_events_error *err, struct perf_pmu *fake_pmu,
		   char *pmu_name)
{
	struct parse_events_state parse_state = {
		.list	  = LIST_HEAD_INIT(parse_state.list),
		...
	};

	ret = parse_events__scanner(str, &parse_state);
	perf_pmu__parse_cleanup();

	if (!ret && list_empty(&parse_state.list)) {
		WARN_ONCE(true, "WARNING: event parser found nothing\n");
		return -1;
	}
	...
}

When returning to the first __parse_events,'parse_state.list' is an empty list so it would return 
"WARNING: event parser found nothing".

So in my patch, I pass a list pointer in and the new created evsels will be added to this list.

>>
>> __parse_events(evlist, str, NULL, NULL);
>> Add the evsels in evlist to the tail of list (the parameter 'list')
>> evlist__delete(evlist);
>>
>> Is my understanding correct?
>>
>> Yes, we have to change the interface of __parse_events() by adding a new
>> parameter 'pmu_name', which will bring much more changes. I agree to make
>> this change in follow-up patches.
> 
> let's check on this over the next version
>

That's fine, thanks.

Thanks
Jin Yao

> thanks,
> jirka
>