linux-kernel - Re: [PATCH RFC 2/9] perf metrics: Don't iter sys metrics if we already found a CPU match

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Message-ID: <bb828dd4-3c22-7383-008e-ab4f860ed686@oracle.com>
Date:   Mon, 3 Jul 2023 14:09:05 +0100
From:   John Garry <john.g.garry@...cle.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     acme@...nel.org, namhyung@...nel.org, jolsa@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        renyu.zj@...ux.alibaba.com, shangxiaojing@...wei.com,
        zhangshaokun@...ilicon.com, qiangqing.zhang@....com,
        kjain@...ux.ibm.com, kan.liang@...ux.intel.com
Subject: Re: [PATCH RFC 2/9] perf metrics: Don't iter sys metrics if we
 already found a CPU match

On 30/06/2023 18:41, Ian Rogers wrote:
> On Wed, Jun 28, 2023 at 3:30 AM John Garry<john.g.garry@...cle.com>  wrote:
>> In metricgroup__add_metric() we still iter the sys metrics if we already
>> found a match from the CPU table, which is pretty pointless, so don't
>> bother.
>>
>> Signed-off-by: John Garry<john.g.garry@...cle.com>
>> ---
>>   tools/perf/util/metricgroup.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
>> index 4389ccd29fe7..8d2ac2513530 100644
>> --- a/tools/perf/util/metricgroup.c
>> +++ b/tools/perf/util/metricgroup.c
>> @@ -1261,6 +1261,12 @@ static int metricgroup__add_metric(const char *pmu, const char *metric_name, con
>>
>>                  has_match = data.has_match;
>>          }

Hi Ian,

>> +
>> +       if (has_match) {
>> +               ret = 0;
>> +               goto out;
>> +       }
>> +
> I think this can just be:
> 
> if (!has_match)

But ret has no initial value

> 
> However, I'm not sure I agree with the intent of the change. We may
> have a metric like IPC and want it to apply to all types of CPU, GPU,
> etc. If we short-cut here then that won't be possible.

A few points to make on this:
- Currently we don't have any same-named metrics like this, so not much 
use in supporting it in the code (yet).
- Even if we had some same-named metrics, I am not sure if it even works 
properly. Do we have any uncore PMU metrics which have same name as CPU 
metrics?
- Further to the previous point, do we really want same-named metrics 
for different PMUs in the future? I think event / metric names need to 
be chosen carefully to avoid clash for other PMUs or keywords. For your 
example, if I did ask for IPC metric, I'd like to be able to just know 
I'm getting IPC metric for CPUs or some other PMUs, but not both.

Thanks,
John

>