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Message-ID: <CAP-5=fU8=-Bj7i-WUXfm8qJYDN3B=91VTmMFstEoZ2ub5MZw8w@mail.gmail.com>
Date: Fri, 31 Oct 2025 12:21:27 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
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
On Fri, Oct 31, 2025 at 11:39 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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)) ?
Yeah, that's me trying to make the code less racy. Will fix in v4.
> And it's not released.
It's just a global leak for the sake of performance, similar to pmus, ...
Thanks,
Ian
> 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
> >
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