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

[Jin, Yao]

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