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

[John Garry]

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