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

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Message-ID: <49025439-f9e3-0d32-b0a3-ff9f9ff71835@huawei.com>
Date:   Tue, 6 Apr 2021 14:21:11 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.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 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