linux-kernel - Re: [PATCH v3] perf s390-sample-raw: Cache counter names

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Message-ID: <aQUCVvIEC7brqaG-@google.com>
Date: Fri, 31 Oct 2025 11:39:18 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Thomas Richter <tmricht@...ux.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] perf s390-sample-raw: Cache counter names

Hi Ian,

On Fri, Oct 31, 2025 at 09:12:13AM -0700, Ian Rogers wrote:
> Searching all event names is slower now that legacy names are
> included. Add a cache to avoid long iterative searches.
> 
> Reported-by: Thomas Richter <tmricht@...ux.ibm.com>
> Closes: https://lore.kernel.org/linux-perf-users/09943f4f-516c-4b93-877c-e4a64ed61d38@linux.ibm.com/
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
> v3: Fix minor comment typo, add Thomas' tag.
> v2: Small tweak to the cache_key, just make it match the wanted event value.
> ---
>  tools/perf/util/s390-sample-raw.c | 56 ++++++++++++++++++++++++++++---
>  1 file changed, 51 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/s390-sample-raw.c b/tools/perf/util/s390-sample-raw.c
> index 335217bb532b..4f269ea7c93b 100644
> --- a/tools/perf/util/s390-sample-raw.c
> +++ b/tools/perf/util/s390-sample-raw.c
> @@ -19,12 +19,14 @@
>  
>  #include <sys/stat.h>
>  #include <linux/compiler.h>
> +#include <linux/err.h>
>  #include <asm/byteorder.h>
>  
>  #include "debug.h"
>  #include "session.h"
>  #include "evlist.h"
>  #include "color.h"
> +#include "hashmap.h"
>  #include "sample-raw.h"
>  #include "s390-cpumcf-kernel.h"
>  #include "util/pmu.h"
> @@ -132,8 +134,8 @@ static int get_counterset_start(int setnr)
>  }
>  
>  struct get_counter_name_data {
> -	int wanted;
> -	char *result;
> +	long wanted;
> +	const char *result;
>  };
>  
>  static int get_counter_name_callback(void *vdata, struct pmu_event_info *info)
> @@ -151,12 +153,22 @@ static int get_counter_name_callback(void *vdata, struct pmu_event_info *info)
>  
>  	rc = sscanf(event_str, "event=%x", &event_nr);
>  	if (rc == 1 && event_nr == data->wanted) {
> -		data->result = strdup(info->name);
> +		data->result = info->name;
>  		return 1; /* Terminate the search. */
>  	}
>  	return 0;
>  }
>  
> +static size_t get_counter_name_hash_fn(long key, void *ctx __maybe_unused)
> +{
> +	return key;
> +}
> +
> +static bool get_counter_name_hashmap_equal_fn(long key1, long key2, void *ctx __maybe_unused)
> +{
> +	return key1 == key2;
> +}
> +
>  /* Scan the PMU and extract the logical name of a counter from the event. Input
>   * is the counter set and counter number with in the set. Construct the event
>   * number and use this as key. If they match return the name of this counter.
> @@ -164,17 +176,51 @@ static int get_counter_name_callback(void *vdata, struct pmu_event_info *info)
>   */
>  static char *get_counter_name(int set, int nr, struct perf_pmu *pmu)
>  {
> +	static struct hashmap *cache;
> +	static struct perf_pmu *cache_pmu;
> +	long cache_key = get_counterset_start(set) + nr;
>  	struct get_counter_name_data data = {
> -		.wanted = get_counterset_start(set) + nr,
> +		.wanted = cache_key,
>  		.result = NULL,
>  	};
> +	char *result = NULL;
>  
>  	if (!pmu)
>  		return NULL;
>  
> +	if (cache_pmu == pmu && hashmap__find(cache, cache_key, &result))
> +		return strdup(result);
> +
>  	perf_pmu__for_each_event(pmu, /*skip_duplicate_pmus=*/ true,
>  				 &data, get_counter_name_callback);
> -	return data.result;
> +
> +	if (data.result)
> +		result = strdup(data.result);
> +
> +	if (cache_pmu == NULL) {
> +		struct hashmap *tmp = hashmap__new(get_counter_name_hash_fn,
> +						   get_counter_name_hashmap_equal_fn,
> +						   /*ctx=*/NULL);
> +
> +		if (!IS_ERR(cache)) {

Shouldn't it be if (!IS_ERR(tmp)) ?

And it's not released.

Thanks,
Namhyung

> +			cache = tmp;
> +			cache_pmu = pmu;
> +		}
> +	}
> +
> +	if (cache_pmu == pmu) {
> +		char *old_value = NULL, *new_value = strdup(result);
> +
> +		if (new_value) {
> +			hashmap__set(cache, cache_key, new_value, /*old_key=*/NULL, &old_value);
> +			/*
> +			 * Free in case of a race, but resizing would be broken
> +			 * in that case.
> +			 */
> +			free(old_value);
> +		}
> +	}
> +	return result;
>  }
>  
>  static void s390_cpumcfdg_dump(struct perf_pmu *pmu, struct perf_sample *sample)
> -- 
> 2.51.1.930.gacf6e81ea2-goog
>