linux-kernel - Re: [PATCH] perf pmu: Fix event list for uncore PMUs

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Date:   Tue, 21 Dec 2021 10:14:42 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <namhyung@...nel.org>, <irogers@...gle.com>,
        <kan.liang@...ux.intel.com>, <linux-perf-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf pmu: Fix event list for uncore PMUs

On 21/12/2021 09:35, Jiri Olsa wrote:
> On Tue, Dec 21, 2021 at 09:10:37AM +0000, John Garry wrote:
>> On 21/12/2021 07:58, Jiri Olsa wrote:
>>>> +	/* Different names -> never duplicates */
>>>> +	if (strcmp(alias_a->name, alias_b->name))
>>>> +		return false;
>>>> +	if (!alias_a->pmu)
>>>> +		return true;
>>>> +	if (!alias_b->pmu)
>>>> +		return true;
>>> nit could be:
>>>
>>> 	if (!alias_a->pmu || !alias_b->pmu)
>>> 		return true;
>>>
>>> would be great to have more comments explaining the check
>>>
>>
>> This is just a sanity check that both strings are non-NULL as we do a
>> strcmp() next. So would this be better:
>>
>> if (!alias_a->pmu || !alias_b->pmu || !strcmp(alias_a->pmu, alias_b->pmu))
>> 	return true
>>
>> ?
>>
>> It will spill a line.
> 
> sure, it cought my eye because the is_cpu check later is done on
> the same line, so I started wondering what's the difference ;-)
> 

Now thinking a bit more I am not confident that this patch is a full fix.

arm have heterogeneous CPU systems as well - which are not "hybrid" - 
and I need to ensure that aliasing is still working properly there, as I 
think that this following check would stop removing duplicates there:

+	/* uncore PMUs */
+	if (!alias_a->is_cpu && !alias_b->is_cpu)
+		return true;
+	return false;

Thanks,
John