Re: [PATCH v2 2/6] perf test: Handle metric reuse in pmu-events parsing test

John Garry
2021-04-06T13:23:45Z

On 06/04/2021 13:55, Jiri Olsa wrote:
>>>> So expr__find_other() may add a new item to pctx->ids, and we always iterate
>>>> again, and try to lookup any pmu_events, *, above. If none exist, then we
>>> hm, I don't see that.. so, what you do is:
>>>
>>> hashmap__for_each_entry_safe((&pctx->ids) ....) {
>>>
>>> rc = expr__find_other(pe->metric_expr, NULL, pctx, 0);
>>> }
>>>
>>> and what I think we need to do is:
>>>
>>> hashmap__for_each_entry_safe((&pctx->ids) ....) {
>>>
>>> rc = expr__find_other(pe->metric_expr, NULL, pctx, 0);
>>>
>>> break;
>>> }
>>>
>>> each time you resolve another metric, you need to restart
>>> the pctx->ids iteration, because there will be new items,
>>> and we are in the middle of it
>> Sure, but we will restart anyway.
> hum, where? you call expr__find_other and continue to next
> pctx->ids item

We have:

resolve_metric_simple()
{
bool all;

do {
all = true;

hashmap__for_each_entry_safe(&pctx->ids, ...) {

pe = metricgroup_find_metric(cur->key, map);
if (!pe)
continue;

...
all = false;

expr_del_id(pctx, cur->key);

...
rc = expr__find_other(pe->metric_expr, pctx);
if (rc)
goto out_err;
}

} while (!all);

}

So once we evaluate a pmu_event in pctx->ids in @pe, @all is set false,
and we would loop again in the do-while loop, regardless of what
expr__find_other() does (apart from erroring), and so call
hashmap__for_each_entry_safe(&pctx->ids, ) again.

This is really what is done in __resolve_metric() - indeed, I would use
that function directly, but it looks hard to extract that from
metricgroup.c .

Thanks,
John

>
>> Regardless of this, I don't think what I am doing is safe, i.e. adding new
>> items in the middle of the iter, so I will change in the way you suggest.
> it'll always add items in the middle of the iteration