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Message-ID: <CAP-5=fXe43BE3hWoQ1gjxXuQ9OYBTNvMjexrxiyC+SHgP9rTYQ@mail.gmail.com>
Date: Wed, 24 Sep 2025 14:34:26 -0700
From: Ian Rogers <irogers@...gle.com>
To: Thomas Falcon <thomas.falcon@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RESEND][PATCH v2 1/2] perf record: Add ratio-to-prev term
On Tue, Sep 2, 2025 at 9:41 AM Thomas Falcon <thomas.falcon@...el.com> wrote:
>
> Provide ratio-to-prev term which allows the user to
> set the event sample period of two events corresponding
> to a desired ratio. If using on an Intel x86 platform with
> Auto Counter Reload support, also set corresponding event's
> config2 attribute with a bitmask which counters to reset and
> which counters to sample if the desired ratio is met or exceeded.
> On other platforms, only the sample period is affected by the
> ratio-to-prev term.
>
> Signed-off-by: Thomas Falcon <thomas.falcon@...el.com>
> ---
> tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
> tools/perf/Documentation/perf-list.txt | 2 +
> tools/perf/arch/x86/util/evsel.c | 53 ++++++++++++++++++
> tools/perf/util/evsel.c | 76 ++++++++++++++++++++++++++
> tools/perf/util/evsel.h | 1 +
> tools/perf/util/evsel_config.h | 1 +
> tools/perf/util/parse-events.c | 22 ++++++++
> tools/perf/util/parse-events.h | 3 +-
> tools/perf/util/parse-events.l | 1 +
> tools/perf/util/pmu.c | 3 +-
> 10 files changed, 213 insertions(+), 2 deletions(-)
> create mode 100644 tools/perf/Documentation/intel-acr.txt
>
> diff --git a/tools/perf/Documentation/intel-acr.txt b/tools/perf/Documentation/intel-acr.txt
> new file mode 100644
> index 000000000000..72654fdd9a52
> --- /dev/null
> +++ b/tools/perf/Documentation/intel-acr.txt
> @@ -0,0 +1,53 @@
> +Intel Auto Counter Reload Support
> +---------------------------------
> +Support for Intel Auto Counter Reload in perf tools
> +
> +Auto counter reload provides a means for software to specify to hardware
> +that certain counters, if supported, should be automatically reloaded
> +upon overflow of chosen counters. By taking a sample only if the rate of
> +one event exceeds some threshold relative to the rate of another event,
> +this feature enables software to sample based on the relative rate of
> +two or more events. To enable this, the user must provide a sample period
> +term and a bitmask ("acr_mask") for each relevant event specifying the
> +counters in an event group to reload if the event's specified sample
> +period is exceeded.
> +
> +For example, if the user desires to measure a scenario when IPC > 2,
> +the event group might look like the one below:
> +
> + perf record -e {cpu_atom/instructions,period=200000,acr_mask=0x2/, \
> + cpu_atom/cycles,period=100000,acr_mask=0x3/} -- true
> +
> +In this case, if the "instructions" counter exceeds the sample period of
> +200000, the second counter, "cycles", will be reset and a sample will be
> +taken. If "cycles" is exceeded first, both counters in the group will be
> +reset. In this way, samples will only be taken for cases where IPC > 2.
> +
> +The acr_mask term is a hexadecimal value representing a bitmask of the
> +events in the group to be reset when the period is exceeded. In the
> +example above, "instructions" is assigned an acr_mask of 0x2, meaning
> +only the second event in the group is reloaded and a sample is taken
> +for the first event. "cycles" is assigned an acr_mask of 0x3, meaning
> +that both event counters will be reset if the sample period is exceeded
> +first.
This is great! Thank you for adding it.
> +
> +ratio-to-prev Event Term
> +------------------------
> +To simplify this, an event term "ratio-to-prev" is provided which is used
> +alongside the sample period term n or the -c/--count option. This would
> +allow users to specify the desired relative rate between events as a
> +ratio. Note: Both events compared must belong to the same PMU.
> +
> +The command above would then become
> +
> + perf record -e {cpu_atom/instructions/, \
> + cpu_atom/cycles,period=100000,ratio-to-prev=0.5/} -- true
> +
> +ratio-to-prev is the ratio of the event using the term relative
> +to the previous event in the group, which will always be 1,
> +for a 1:0.5 or 2:1 ratio.
> +
> +To sample for IPC < 2 for example, the events need to be reordered:
> +
> + perf record -e {cpu_atom/cycles/, \
> + cpu_atom/instructions,period=200000,ratio-to-prev=2.0/} -- true
> diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt
> index 28215306a78a..10bc66d39202 100644
> --- a/tools/perf/Documentation/perf-list.txt
> +++ b/tools/perf/Documentation/perf-list.txt
> @@ -392,6 +392,8 @@ Support raw format:
> . '--raw-dump [hw|sw|cache|tracepoint|pmu|event_glob]', shows the raw-dump of
> a certain kind of events.
>
> +include::intel-acr.txt[]
> +
> SEE ALSO
> --------
> linkperf:perf-stat[1], linkperf:perf-top[1],
> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
> index 9bc80fff3aa0..84858e4c397d 100644
> --- a/tools/perf/arch/x86/util/evsel.c
> +++ b/tools/perf/arch/x86/util/evsel.c
> @@ -1,7 +1,9 @@
> // SPDX-License-Identifier: GPL-2.0
> #include <stdio.h>
> #include <stdlib.h>
> +#include "util/evlist.h"
> #include "util/evsel.h"
> +#include "util/evsel_config.h"
> #include "util/env.h"
> #include "util/pmu.h"
> #include "util/pmus.h"
> @@ -67,6 +69,57 @@ int arch_evsel__hw_name(struct evsel *evsel, char *bf, size_t size)
> event_name);
> }
>
> +void arch_evsel__apply_ratio_to_prev(struct evsel *evsel,
> + struct perf_event_attr *attr)
> +{
> + struct perf_event_attr *prev_attr = NULL;
> + struct evsel *evsel_prev = NULL;
> + const char *name = "acr_mask";
> + int evsel_idx = 0;
> + __u64 ev_mask, pr_ev_mask;
> +
> + if (!perf_pmu__has_format(evsel->pmu, name)) {
> + pr_err("'%s' does not have acr_mask format support\n", evsel->pmu->name);
> + return;
> + }
> + if (perf_pmu__format_type(evsel->pmu, name) !=
> + PERF_PMU_FORMAT_VALUE_CONFIG2) {
> + pr_err("'%s' does not have config2 format support\n", evsel->pmu->name);
> + return;
> + }
> +
> + evsel_prev = evsel__prev(evsel);
> + if (!evsel_prev) {
> + pr_err("Previous event does not exist.\n");
> + return;
> + }
Nit: you should probably check that the leader of both events is the
same, this means the events are in the same group.
> +
> + prev_attr = &evsel_prev->core.attr;
> +
> + if (prev_attr->config2) {
> + pr_err("'%s' has set config2 (acr_mask?) already, configuration not supported\n", evsel_prev->name);
> + return;
> + }
> +
> + /*
> + * acr_mask (config2) is calculated using the event's index in
> + * the event group. The first event will use the index of the
> + * second event as its mask (e.g., 0x2), indicating that the
> + * second event counter will be reset and a sample taken for
> + * the first event if its counter overflows. The second event
> + * will use the mask consisting of the first and second bits
> + * (e.g., 0x3), meaning both counters will be reset if the
> + * second event counter overflows.
> + */
> +
> + evsel_idx = evsel__group_idx(evsel);
> + ev_mask = 1ull << evsel_idx;
> + pr_ev_mask = 1ull << (evsel_idx - 1);
> +
> + prev_attr->config2 = ev_mask;
> + attr->config2 = ev_mask | pr_ev_mask;
> +}
> +
> static void ibs_l3miss_warn(void)
> {
> pr_warning(
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index d264c143b592..f6f93920c0aa 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1091,6 +1091,71 @@ static void evsel__reset_callgraph(struct evsel *evsel, struct callchain_param *
> }
> }
>
> +static void evsel__apply_ratio_to_prev(struct evsel *evsel,
> + struct perf_event_attr *attr,
> + struct record_opts *opts,
> + const char *buf)
> +{
> + struct perf_event_attr *prev_attr = NULL;
> + struct evsel *evsel_prev = NULL;
> + u64 type = evsel->core.attr.sample_type;
> + u64 prev_type = 0;
> + double rtp;
> +
> + rtp = strtod(buf, NULL);
> + if (rtp <= 0) {
> + pr_err("Invalid ratio-to-prev value %lf\n", rtp);
> + return;
> + }
> + if (evsel == evsel__leader(evsel)) {
> + pr_err("Invalid use of ratio-to-prev term without preceding element in group\n");
> + return;
> + }
Ah, it is done here.
> + if (!evsel->pmu->is_core) {
> + pr_err("Event using ratio-to-prev term must have a core PMU\n");
> + return;
> + }
> +
> + evsel_prev = evsel__prev(evsel);
> + if (!evsel_prev) {
> + pr_err("Previous event does not exist.\n");
> + return;
> + }
> +
> + if (evsel_prev->pmu->type != evsel->pmu->type) {
> + pr_err("Compared events (\"%s\", \"%s\") must have same PMU\n",
> + evsel->name, evsel_prev->name);
> + return;
> + }
> +
> + prev_attr = &evsel_prev->core.attr;
> + prev_type = evsel_prev->core.attr.sample_type;
> +
> + if (!(prev_type & PERF_SAMPLE_PERIOD)) {
> + attr->sample_period = prev_attr->sample_period * rtp;
> + attr->freq = 0;
> + evsel__reset_sample_bit(evsel, PERIOD);
> + } else if (!(type & PERF_SAMPLE_PERIOD)) {
> + prev_attr->sample_period = attr->sample_period / rtp;
> + prev_attr->freq = 0;
> + evsel__reset_sample_bit(evsel_prev, PERIOD);
> + } else {
> + if (opts->user_interval != ULLONG_MAX) {
> + prev_attr->sample_period = opts->user_interval;
> + attr->sample_period = prev_attr->sample_period * rtp;
> + prev_attr->freq = 0;
> + attr->freq = 0;
> + evsel__reset_sample_bit(evsel_prev, PERIOD);
> + evsel__reset_sample_bit(evsel, PERIOD);
> + } else {
> + pr_err("Event period term or count (-c) must be set when using ratio-to-prev term.\n");
> + return;
> + }
> + }
> +
> + arch_evsel__apply_ratio_to_prev(evsel, attr);
> +}
> +
> static void evsel__apply_config_terms(struct evsel *evsel,
> struct record_opts *opts, bool track)
> {
> @@ -1104,6 +1169,7 @@ static void evsel__apply_config_terms(struct evsel *evsel,
> u32 dump_size = 0;
> int max_stack = 0;
> const char *callgraph_buf = NULL;
> + const char *rtp_buf = NULL;
>
> list_for_each_entry(term, config_terms, list) {
> switch (term->type) {
> @@ -1174,6 +1240,9 @@ static void evsel__apply_config_terms(struct evsel *evsel,
> break;
> case EVSEL__CONFIG_TERM_CFG_CHG:
> break;
> + case EVSEL__CONFIG_TERM_RATIO_TO_PREV:
> + rtp_buf = term->val.str;
> + break;
> default:
> break;
> }
> @@ -1225,6 +1294,8 @@ static void evsel__apply_config_terms(struct evsel *evsel,
> evsel__config_callchain(evsel, opts, ¶m);
> }
> }
> + if (rtp_buf)
> + evsel__apply_ratio_to_prev(evsel, attr, opts, rtp_buf);
> }
>
> struct evsel_config_term *__evsel__get_config_term(struct evsel *evsel, enum evsel_term_type type)
> @@ -1249,6 +1320,11 @@ void __weak arch__post_evsel_config(struct evsel *evsel __maybe_unused,
> {
> }
>
> +void __weak arch_evsel__apply_ratio_to_prev(struct evsel *evsel __maybe_unused,
> + struct perf_event_attr *attr __maybe_unused)
> +{
> +}
> +
I'm not a fan of weak functions as they introduce subtle bugs, but I
can see why you have this organization.
Reviewed-by: Ian Rogers <irogers@...gle.com>
Thanks,
Ian
> static void evsel__set_default_freq_period(struct record_opts *opts,
> struct perf_event_attr *attr)
> {
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 5797a02e5d6a..5002c795e818 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -342,6 +342,7 @@ void evsel__set_sample_id(struct evsel *evsel, bool use_sample_identifier);
> void arch_evsel__set_sample_weight(struct evsel *evsel);
> void arch__post_evsel_config(struct evsel *evsel, struct perf_event_attr *attr);
> int arch_evsel__open_strerror(struct evsel *evsel, char *msg, size_t size);
> +void arch_evsel__apply_ratio_to_prev(struct evsel *evsel, struct perf_event_attr *attr);
>
> int evsel__set_filter(struct evsel *evsel, const char *filter);
> int evsel__append_tp_filter(struct evsel *evsel, const char *filter);
> diff --git a/tools/perf/util/evsel_config.h b/tools/perf/util/evsel_config.h
> index 94a1e9cf73d6..bcd3a978f0c4 100644
> --- a/tools/perf/util/evsel_config.h
> +++ b/tools/perf/util/evsel_config.h
> @@ -28,6 +28,7 @@ enum evsel_term_type {
> EVSEL__CONFIG_TERM_AUX_ACTION,
> EVSEL__CONFIG_TERM_AUX_SAMPLE_SIZE,
> EVSEL__CONFIG_TERM_CFG_CHG,
> + EVSEL__CONFIG_TERM_RATIO_TO_PREV,
> };
>
> struct evsel_config_term {
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 8282ddf68b98..850de3a51f47 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -834,6 +834,7 @@ const char *parse_events__term_type_str(enum parse_events__term_type term_type)
> [PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE] = "legacy-cache",
> [PARSE_EVENTS__TERM_TYPE_HARDWARE] = "hardware",
> [PARSE_EVENTS__TERM_TYPE_CPU] = "cpu",
> + [PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV] = "ratio-to-prev",
> };
> if ((unsigned int)term_type >= __PARSE_EVENTS__TERM_TYPE_NR)
> return "unknown term";
> @@ -884,6 +885,7 @@ config_term_avail(enum parse_events__term_type term_type, struct parse_events_er
> case PARSE_EVENTS__TERM_TYPE_RAW:
> case PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE:
> case PARSE_EVENTS__TERM_TYPE_HARDWARE:
> + case PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> default:
> if (!err)
> return false;
> @@ -1037,6 +1039,21 @@ do { \
> perf_cpu_map__put(map);
> break;
> }
> + case PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> + CHECK_TYPE_VAL(STR);
> + if (strtod(term->val.str, NULL) <= 0) {
> + parse_events_error__handle(err, term->err_val,
> + strdup("zero or negative"),
> + NULL);
> + return -EINVAL;
> + }
> + if (errno == ERANGE) {
> + parse_events_error__handle(err, term->err_val,
> + strdup("too big"),
> + NULL);
> + return -EINVAL;
> + }
> + break;
> case PARSE_EVENTS__TERM_TYPE_DRV_CFG:
> case PARSE_EVENTS__TERM_TYPE_USER:
> case PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE:
> @@ -1165,6 +1182,7 @@ static int config_term_tracepoint(struct perf_event_attr *attr,
> case PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE:
> case PARSE_EVENTS__TERM_TYPE_HARDWARE:
> case PARSE_EVENTS__TERM_TYPE_CPU:
> + case PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> default:
> if (err) {
> parse_events_error__handle(err, term->err_term,
> @@ -1289,6 +1307,9 @@ do { \
> ADD_CONFIG_TERM_VAL(AUX_SAMPLE_SIZE, aux_sample_size,
> term->val.num, term->weak);
> break;
> + case PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> + ADD_CONFIG_TERM_STR(RATIO_TO_PREV, term->val.str, term->weak);
> + break;
> case PARSE_EVENTS__TERM_TYPE_USER:
> case PARSE_EVENTS__TERM_TYPE_CONFIG:
> case PARSE_EVENTS__TERM_TYPE_CONFIG1:
> @@ -1355,6 +1376,7 @@ static int get_config_chgs(struct perf_pmu *pmu, struct parse_events_terms *head
> case PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE:
> case PARSE_EVENTS__TERM_TYPE_HARDWARE:
> case PARSE_EVENTS__TERM_TYPE_CPU:
> + case PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> default:
> break;
> }
> diff --git a/tools/perf/util/parse-events.h b/tools/perf/util/parse-events.h
> index 62dc7202e3ba..b2dcc52e3814 100644
> --- a/tools/perf/util/parse-events.h
> +++ b/tools/perf/util/parse-events.h
> @@ -83,7 +83,8 @@ enum parse_events__term_type {
> PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE,
> PARSE_EVENTS__TERM_TYPE_HARDWARE,
> PARSE_EVENTS__TERM_TYPE_CPU,
> -#define __PARSE_EVENTS__TERM_TYPE_NR (PARSE_EVENTS__TERM_TYPE_CPU + 1)
> + PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV,
> +#define __PARSE_EVENTS__TERM_TYPE_NR (PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV + 1)
> };
>
> struct parse_events_term {
> diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
> index 2034590eb789..25206de68007 100644
> --- a/tools/perf/util/parse-events.l
> +++ b/tools/perf/util/parse-events.l
> @@ -336,6 +336,7 @@ aux-action { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_AUX_ACTION); }
> aux-sample-size { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_AUX_SAMPLE_SIZE); }
> metric-id { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_METRIC_ID); }
> cpu { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CPU); }
> +ratio-to-prev { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV); }
> cpu-cycles|cycles { return hw_term(yyscanner, PERF_COUNT_HW_CPU_CYCLES); }
> stalled-cycles-frontend|idle-cycles-frontend { return hw_term(yyscanner, PERF_COUNT_HW_STALLED_CYCLES_FRONTEND); }
> stalled-cycles-backend|idle-cycles-backend { return hw_term(yyscanner, PERF_COUNT_HW_STALLED_CYCLES_BACKEND); }
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index 5a291f1380ed..3d1f975e8db9 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -1541,7 +1541,7 @@ static int pmu_config_term(const struct perf_pmu *pmu,
> break;
> case PARSE_EVENTS__TERM_TYPE_USER: /* Not hardcoded. */
> return -EINVAL;
> - case PARSE_EVENTS__TERM_TYPE_NAME ... PARSE_EVENTS__TERM_TYPE_CPU:
> + case PARSE_EVENTS__TERM_TYPE_NAME ... PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV:
> /* Skip non-config terms. */
> break;
> default:
> @@ -1930,6 +1930,7 @@ int perf_pmu__for_each_format(struct perf_pmu *pmu, void *state, pmu_format_call
> "aux-action=(pause|resume|start-paused)",
> "aux-sample-size=number",
> "cpu=number",
> + "ratio-to-prev=string",
> };
> struct perf_pmu_format *format;
> int ret;
> --
> 2.50.1
>
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