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

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Message-ID: <f5b209b2-1e9e-ebad-b2ed-eda9fe858ec8@huawei.com>
Date:   Tue, 6 Apr 2021 13:43:09 +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 13:17, Jiri Olsa wrote:
>>>> +			ref = &metric->metric_ref;
>>>> +			ref->metric_name = pe->metric_name;
>>>> +			ref->metric_expr = pe->metric_expr;
>>>> +			list_add_tail(&metric->list, compound_list);
>>>> +
>>>> +			rc = expr__find_other(pe->metric_expr, NULL, pctx, 0);
>> Hi Jirka,
>>
>>> so this might add new items to pctx->ids, I think you need
>>> to restart the iteration as we do it in __resolve_metric
>>> otherwise you could miss some new keys
>> I thought that I was doing this. Indeed, this code is very much like
>> __resolve_metric();)
>>
>> 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.

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.

Thanks,
John