linux-kernel - Re: [PATCH v4 13/17] perf pmu-events: Don't assume pmu

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Message-ID: <93448cc1-7b21-3b04-92d2-65d61ba140fe@huawei.com>
Date:   Fri, 5 Aug 2022 13:56:04 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ian Rogers <irogers@...gle.com>, Will Deacon <will@...nel.org>,
        "James Clark" <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        "Kan Liang" <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>
CC:     Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v4 13/17] perf pmu-events: Don't assume pmu_event is an
 array

On 04/08/2022 23:18, Ian Rogers wrote:
> Current code assumes that a struct pmu_event can be iterated over
> forward until a NULL pmu_event is encountered. This makes it difficult
> to refactor pmu_event. Add a loop function taking a callback function
> that's passed the struct pmu_event. This way the pmu_event is only
> needed for one element and not an entire array.
> 
> Switch existing code iterating over the pmu_event arrays to use the new
> loop function pmu_events_table_for_each_event.


I find it hard to follow the change from the description. The title is 
"Don't assume pmu_event is an array", but that is rightly what 
pmu_events_table_for_each_event() does.

If I check - for exmaple - pmu_add_cpu_aliases_map(), you just switch it 
over to using pmu_events_table_for_each_event(), which seems resonable. 
So it just seems here that we're refactoring the code, and not changing 
the nature of how we handle pmu_events *.

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>   tools/perf/pmu-events/empty-pmu-events.c |  34 +++--
>   tools/perf/pmu-events/jevents.py         |  34 +++--
>   tools/perf/pmu-events/pmu-events.h       |   3 +
>   tools/perf/tests/pmu-events.c            | 136 +++++++++--------
>   tools/perf/util/metricgroup.c            | 181 ++++++++++++++++-------
>   tools/perf/util/pmu.c                    |  65 ++++----
>   tools/perf/util/s390-sample-raw.c        |  42 ++++--
>   7 files changed, 313 insertions(+), 182 deletions(-)
> 
> diff --git a/tools/perf/pmu-events/empty-pmu-events.c b/tools/perf/pmu-events/empty-pmu-events.c
> index 028f44efe48d..bee1967baa2b 100644
> --- a/tools/perf/pmu-events/empty-pmu-events.c
> +++ b/tools/perf/pmu-events/empty-pmu-events.c
> @@ -247,6 +247,20 @@ static const struct pmu_sys_events pmu_sys_event_tables[] = {
>   	},
>   };
>   
> +int pmu_events_table_for_each_event(const struct pmu_event *table, pmu_event_iter_fn fn,
> +				    void *data)
> +{
> +	for (const struct pmu_event *pe = &table[0];
> +	     pe->name || pe->metric_group || pe->metric_name;
> +	     pe++) {
> +		int ret = fn(pe, table, data);
> +
> +		if (ret)
> +			return ret;
> +	}
> +	return 0;
> +}
> +
>   const struct pmu_event *perf_pmu__find_table(struct perf_pmu *pmu)
>   {
>   	const struct pmu_event *table = NULL;
> @@ -291,14 +305,10 @@ int pmu_for_each_core_event(pmu_event_iter_fn fn, void *data)
>   	for (const struct pmu_events_map *tables = &pmu_events_map[0];
>   	     tables->table;
>   	     tables++) {
> -		for (const struct pmu_event *pe = &tables->table[0];
> -		     pe->name || pe->metric_group || pe->metric_name;
> -		     pe++) {
> -			int ret = fn(pe, &tables->table[0], data);
> +		int ret = pmu_events_table_for_each_event(tables->table, fn, data);
>   
> -			if (ret)
> -				return ret;
> -		}
> +		if (ret)
> +			return ret;
>   	}
>   	return 0;
>   }
> @@ -319,14 +329,10 @@ int pmu_for_each_sys_event(pmu_event_iter_fn fn, void *data)
>   	for (const struct pmu_sys_events *tables = &pmu_sys_event_tables[0];
>   	     tables->name;
>   	     tables++) {
> -		for (const struct pmu_event *pe = &tables->table[0];
> -		     pe->name || pe->metric_group || pe->metric_name;
> -		     pe++) {
> -			int ret = fn(pe, &tables->table[0], data);
> +		int ret = pmu_events_table_for_each_event(tables->table, fn, data);
>   
> -			if (ret)
> -				return ret;
> -		}
> +		if (ret)
> +			return ret;
>   	}
>   	return 0;
>   }
> diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
> index e976c5e8e80b..365c960202b0 100755
> --- a/tools/perf/pmu-events/jevents.py
> +++ b/tools/perf/pmu-events/jevents.py
> @@ -409,6 +409,20 @@ static const struct pmu_sys_events pmu_sys_event_tables[] = {
>   \t},
>   };
>   
> +int pmu_events_table_for_each_event(const struct pmu_event *table, pmu_event_iter_fn fn,
> +                                    void *data)

Again we seem to be just duplicating what is in empty-pmu-events.c - can 
we avoid this? another idea (apart from linking in other c files) is for 
empty-pmu-events.c to be generated from jevents.py (like how it was done 
for jevents.c)