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

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Date:   Tue, 6 Apr 2021 15:34:16 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     will@...nel.org, mathieu.poirier@...aro.org, leo.yan@...aro.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, irogers@...gle.com, linuxarm@...wei.com,
        kjain@...ux.ibm.com, kan.liang@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        zhangshaokun@...ilicon.com, pc@...ibm.com
Subject: Re: [PATCH v2 2/6] perf test: Handle metric reuse in pmu-events
 parsing test

On Tue, Apr 06, 2021 at 02:21:11PM +0100, John Garry wrote:
> 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.

ah ok, so it finishes the hash iteration first and
then restarts it.. ok, I missed that, then it's fine

> 
> 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 .

yea, it's another world ;-) it's better to keep it separated

thanks,
jirka

> 
> 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
>