[Patch v3 0/2] perf record: ratio-to-prev event term for auto counter reload

[Patch v3 0/2] perf record: ratio-to-prev event term for auto counter reload

[thomas.falcon]

From: Thomas Falcon <thomas.falcon@intel.com>

The Auto Counter Reload (ACR)[1] feature is used to track the
relative rates of two or more perf events, only sampling
when a given threshold is exceeded. This helps reduce overhead
and unnecessary samples. However, enabling this feature
currently requires setting two parameters:

 -- Event sampling period ("period")
 -- acr_mask, which determines which events get reloaded
    when the sample period is reached.

For example, in the following command:

perf record -e "{cpu_atom/branch-misses,period=200000,\
acr_mask=0x2/ppu,cpu_atom/branch-instructions,period=1000000,\
acr_mask=0x3/u}" -- ./mispredict

The goal is to limit event sampling to cases when the
branch miss rate exceeds 20%. If the branch instructions
sample period is exceeded first, both events are reloaded.
If branch misses exceed their threshold first, only the
second counter is reloaded, and a sample is taken.

To simplify this, provide a new “ratio-to-prev” event term
that works alongside the period event option or -c option.
This would allow users to specify the desired relative rate
between events as a ratio, making configuration more intuitive.

With this enhancement, the equivalent command would be:

perf record -e "{cpu_atom/branch-misses/ppu,\
cpu_atom/branch-instructions,period=1000000,ratio_to_prev=5/u}" \
-- ./mispredict

or

perf record -e "{cpu_atom/branch-misses/ppu,\
cpu_atom/branch-instructions,ratio-to-prev=5/u}" -c 1000000 \
-- ./mispredict

[1] https://lore.kernel.org/lkml/20250327195217.2683619-1-kan.liang@linux.intel.com/

v3: rebase to current perf-tools-next

v2: (changes below suggested by Ian Rogers):

-- Add documentation explaining acr_mask bitmask used by ACR
-- Move ACR specific implementation to arch/x86/
-- Provide test cases for event parsing and perf record tests

Thomas Falcon (2):
  perf record: Add ratio-to-prev term
  perf record: Add auto counter reload parse and regression tests

 tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
 tools/perf/Documentation/perf-list.txt |  2 +
 tools/perf/arch/x86/util/evsel.c       | 52 ++++++++++++++++++
 tools/perf/tests/parse-events.c        | 54 ++++++++++++++++++
 tools/perf/tests/shell/record.sh       | 40 ++++++++++++++
 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 +-
 12 files changed, 306 insertions(+), 2 deletions(-)
 create mode 100644 tools/perf/Documentation/intel-acr.txt

-- 
2.50.1

[Patch v3 1/2] perf record: Add ratio-to-prev term

[thomas.falcon]

From: Thomas Falcon <thomas.falcon@intel.com>

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.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Thomas Falcon <thomas.falcon@intel.com>
---
 tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
 tools/perf/Documentation/perf-list.txt |  2 +
 tools/perf/arch/x86/util/evsel.c       | 52 ++++++++++++++++++
 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, 212 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.
+
+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 a5039d1614f9..a4378a0cd914 100644
--- a/tools/perf/Documentation/perf-list.txt
+++ b/tools/perf/Documentation/perf-list.txt
@@ -393,6 +393,8 @@ 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 e67701d26f24..23a8e662a912 100644
--- a/tools/perf/arch/x86/util/evsel.c
+++ b/tools/perf/arch/x86/util/evsel.c
@@ -4,6 +4,7 @@
 #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"
@@ -71,6 +72,57 @@ 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;
+	}
+
+	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 1a29d4f47bbf..56cef1310574 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;
+	}
+	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, &param);
 		}
 	}
+	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)
+{
+}
+
 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 03f9f22e3a0c..521d280c4abe 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -343,6 +343,7 @@ 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, int err, 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 452f12191f6e..da73d686f6b9 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -842,6 +842,7 @@ 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";
@@ -892,6 +893,7 @@ 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;
@@ -1045,6 +1047,21 @@ 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(parse_state->error, term->err_val,
+						   strdup("zero or negative"),
+						   NULL);
+			return -EINVAL;
+		}
+		if (errno == ERANGE) {
+			parse_events_error__handle(parse_state->error, 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:
@@ -1173,6 +1190,7 @@ 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:
 		parse_events_error__handle(parse_state->error, term->err_term,
 					strdup(parse_events__term_type_str(term->type_term)),
@@ -1295,6 +1313,9 @@ 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:
@@ -1361,6 +1382,7 @@ 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 a5c5fc39fd6f..8f8c8e7fbcf1 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 294e943bcdb4..c985aa8a7d56 100644
--- a/tools/perf/util/parse-events.l
+++ b/tools/perf/util/parse-events.l
@@ -337,6 +337,7 @@ 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

Re: [Patch v3 1/2] perf record: Add ratio-to-prev term

[Namhyung Kim]

On Thu, Oct 02, 2025 at 06:43:05PM -0500, thomas.falcon@intel.com wrote:
> From: Thomas Falcon <thomas.falcon@intel.com>
> 
> 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.
> 
> Reviewed-by: Ian Rogers <irogers@google.com>
> Signed-off-by: Thomas Falcon <thomas.falcon@intel.com>
> ---
>  tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
>  tools/perf/Documentation/perf-list.txt |  2 +
>  tools/perf/arch/x86/util/evsel.c       | 52 ++++++++++++++++++
>  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, 212 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.

Thanks for the documentation, now I got the idea what it tries to do.
So acr_mask and ratio-to-prev are only allowed in a group..

> +
> +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.

IIUC bit of 1 means auto-reload without samples and 0 means to take a
sample (as normal), right?  And index is meaningful in a group and not
related to hardware, correct?


> +
> +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.

What about acr_mask?

> +
> +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 a5039d1614f9..a4378a0cd914 100644
> --- a/tools/perf/Documentation/perf-list.txt
> +++ b/tools/perf/Documentation/perf-list.txt
> @@ -393,6 +393,8 @@ 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 e67701d26f24..23a8e662a912 100644
> --- a/tools/perf/arch/x86/util/evsel.c
> +++ b/tools/perf/arch/x86/util/evsel.c
> @@ -4,6 +4,7 @@
>  #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"
> @@ -71,6 +72,57 @@ 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;
> +	}
> +
> +	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);

This line is too long.

Also I'm afraid this only works for two events in a group.

Thanks,
Namhyung


> +		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 1a29d4f47bbf..56cef1310574 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;
> +	}
> +	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, &param);
>  		}
>  	}
> +	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)
> +{
> +}
> +
>  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 03f9f22e3a0c..521d280c4abe 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -343,6 +343,7 @@ 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, int err, 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 452f12191f6e..da73d686f6b9 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -842,6 +842,7 @@ 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";
> @@ -892,6 +893,7 @@ 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;
> @@ -1045,6 +1047,21 @@ 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(parse_state->error, term->err_val,
> +						   strdup("zero or negative"),
> +						   NULL);
> +			return -EINVAL;
> +		}
> +		if (errno == ERANGE) {
> +			parse_events_error__handle(parse_state->error, 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:
> @@ -1173,6 +1190,7 @@ 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:
>  		parse_events_error__handle(parse_state->error, term->err_term,
>  					strdup(parse_events__term_type_str(term->type_term)),
> @@ -1295,6 +1313,9 @@ 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:
> @@ -1361,6 +1382,7 @@ 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 a5c5fc39fd6f..8f8c8e7fbcf1 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 294e943bcdb4..c985aa8a7d56 100644
> --- a/tools/perf/util/parse-events.l
> +++ b/tools/perf/util/parse-events.l
> @@ -337,6 +337,7 @@ 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
> 

Re: [Patch v3 1/2] perf record: Add ratio-to-prev term

[Falcon, Thomas]

On Tue, 2025-10-07 at 17:55 +0900, Namhyung Kim wrote:
> On Thu, Oct 02, 2025 at 06:43:05PM -0500,
> thomas.falcon@intel.com wrote:
> > From: Thomas Falcon <thomas.falcon@intel.com>
> > 
> > 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.
> > 
> > Reviewed-by: Ian Rogers <irogers@google.com>
> > Signed-off-by: Thomas Falcon <thomas.falcon@intel.com>
> > ---
> >  tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
> >  tools/perf/Documentation/perf-list.txt |  2 +
> >  tools/perf/arch/x86/util/evsel.c       | 52 ++++++++++++++++++
> >  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, 212 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.
> 
> Thanks for the documentation, now I got the idea what it tries to do.
> So acr_mask and ratio-to-prev are only allowed in a group..

Hi, yes, that's right.

> 
> > +
> > +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.
> 
> IIUC bit of 1 means auto-reload without samples and 0 means to take a
> sample (as normal), right?  And index is meaningful in a group and
> not
> related to hardware, correct?
> 

Yes. Maybe I can update to make that clearer in the future.

> 
> > +
> > +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.
> 
> What about acr_mask?

In this case, the event using ratio-to-prev term, 'cycles', will reload
both event counters if the sample period is exceeded first, so the
acr_mask would be 0b11 or 0x3. The other event, 'instructions', will
have an acr_mask of 0b10 or 0x2, meaning it will be reloaded and an
sample is taken for 'cycles.'

> 
> > +
> > +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 a5039d1614f9..a4378a0cd914 100644
> > --- a/tools/perf/Documentation/perf-list.txt
> > +++ b/tools/perf/Documentation/perf-list.txt
> > @@ -393,6 +393,8 @@ 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 e67701d26f24..23a8e662a912 100644
> > --- a/tools/perf/arch/x86/util/evsel.c
> > +++ b/tools/perf/arch/x86/util/evsel.c
> > @@ -4,6 +4,7 @@
> >  #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"
> > @@ -71,6 +72,57 @@ 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;
> > +	}
> > +
> > +	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);
> 
> This line is too long.

Thanks, I will submit a cleanup soon.

> 
> Also I'm afraid this only works for two events in a group.

For now support is limited to two events in a group. For larger groups,
the acr_mask and period terms can be used.

Thanks,
Tom

> 
> Thanks,
> Namhyung
> 
> 
> > +		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 1a29d4f47bbf..56cef1310574 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;
> > +	}
> > +	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,
> > &param);
> >  		}
> >  	}
> > +	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)
> > +{
> > +}
> > +
> >  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 03f9f22e3a0c..521d280c4abe 100644
> > --- a/tools/perf/util/evsel.h
> > +++ b/tools/perf/util/evsel.h
> > @@ -343,6 +343,7 @@ 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, int err, 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 452f12191f6e..da73d686f6b9 100644
> > --- a/tools/perf/util/parse-events.c
> > +++ b/tools/perf/util/parse-events.c
> > @@ -842,6 +842,7 @@ 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";
> > @@ -892,6 +893,7 @@ 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;
> > @@ -1045,6 +1047,21 @@ 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(parse_state-
> > >error, term->err_val,
> > +						   strdup("zero or
> > negative"),
> > +						   NULL);
> > +			return -EINVAL;
> > +		}
> > +		if (errno == ERANGE) {
> > +			parse_events_error__handle(parse_state-
> > >error, 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:
> > @@ -1173,6 +1190,7 @@ 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:
> >  		parse_events_error__handle(parse_state->error,
> > term->err_term,
> >  					strdup(parse_events__term_
> > type_str(term->type_term)),
> > @@ -1295,6 +1313,9 @@ 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:
> > @@ -1361,6 +1382,7 @@ 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 a5c5fc39fd6f..8f8c8e7fbcf1 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 294e943bcdb4..c985aa8a7d56 100644
> > --- a/tools/perf/util/parse-events.l
> > +++ b/tools/perf/util/parse-events.l
> > @@ -337,6 +337,7 @@ 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
> > 
> 

[Patch v3 2/2] perf record: Add auto counter reload parse and regression tests

[thomas.falcon]

From: Thomas Falcon <thomas.falcon@intel.com>

Include event parsing and regression tests for auto counter reload
and ratio-to-prev event term.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Thomas Falcon <thomas.falcon@intel.com>
---
 tools/perf/tests/parse-events.c  | 54 ++++++++++++++++++++++++++++++++
 tools/perf/tests/shell/record.sh | 40 +++++++++++++++++++++++
 2 files changed, 94 insertions(+)

diff --git a/tools/perf/tests/parse-events.c b/tools/perf/tests/parse-events.c
index bb8004397650..67550cc60555 100644
--- a/tools/perf/tests/parse-events.c
+++ b/tools/perf/tests/parse-events.c
@@ -1736,6 +1736,53 @@ static int test__intel_pt(struct evlist *evlist)
 	return TEST_OK;
 }
 
+static bool test__acr_valid(void)
+{
+	struct perf_pmu *pmu = NULL;
+
+	while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
+		if (perf_pmu__has_format(pmu, "acr_mask"))
+			return true;
+	}
+
+	return false;
+}
+
+static int test__ratio_to_prev(struct evlist *evlist)
+{
+	struct evsel *evsel;
+	int ret;
+
+	TEST_ASSERT_VAL("wrong number of entries", 2 * perf_pmus__num_core_pmus() == evlist->core.nr_entries);
+
+	 evlist__for_each_entry(evlist, evsel) {
+		if (!perf_pmu__has_format(evsel->pmu, "acr_mask"))
+			return TEST_OK;
+
+		if (evsel == evlist__first(evlist)) {
+			TEST_ASSERT_VAL("wrong config2", 0 == evsel->core.attr.config2);
+			TEST_ASSERT_VAL("wrong leader", evsel__is_group_leader(evsel));
+			TEST_ASSERT_VAL("wrong core.nr_members", evsel->core.nr_members == 2);
+			TEST_ASSERT_VAL("wrong group_idx", evsel__group_idx(evsel) == 0);
+			ret = assert_hw(&evsel->core, PERF_COUNT_HW_CPU_CYCLES, "cycles");
+		} else {
+			TEST_ASSERT_VAL("wrong config2", 0 == evsel->core.attr.config2);
+			TEST_ASSERT_VAL("wrong leader", !evsel__is_group_leader(evsel));
+			TEST_ASSERT_VAL("wrong core.nr_members", evsel->core.nr_members == 0);
+			TEST_ASSERT_VAL("wrong group_idx", evsel__group_idx(evsel) == 1);
+			ret = assert_hw(&evsel->core, PERF_COUNT_HW_INSTRUCTIONS, "instructions");
+		}
+		if (ret)
+			return ret;
+		/*
+		 * The period value gets configured within evlist__config,
+		 * while this test executes only parse events method.
+		 */
+		TEST_ASSERT_VAL("wrong period", 0 == evsel->core.attr.sample_period);
+	}
+	return TEST_OK;
+}
+
 static int test__checkevent_complex_name(struct evlist *evlist)
 {
 	struct evsel *evsel = evlist__first(evlist);
@@ -2249,6 +2296,13 @@ static const struct evlist_test test__events[] = {
 		.check = test__checkevent_tracepoint,
 		/* 4 */
 	},
+	{
+		.name  = "{cycles,instructions/period=200000,ratio-to-prev=2.0/}",
+		.valid = test__acr_valid,
+		.check = test__ratio_to_prev,
+		/* 5 */
+	},
+
 };
 
 static const struct evlist_test test__events_pmu[] = {
diff --git a/tools/perf/tests/shell/record.sh b/tools/perf/tests/shell/record.sh
index b1ad24fb3b33..0f5841c479e7 100755
--- a/tools/perf/tests/shell/record.sh
+++ b/tools/perf/tests/shell/record.sh
@@ -388,6 +388,45 @@ test_callgraph() {
   echo "Callgraph test [Success]"
 }
 
+test_ratio_to_prev() {
+  echo "ratio-to-prev test"
+  if ! perf record -o /dev/null -e "{instructions, cycles/period=100000,ratio-to-prev=0.5/}" \
+     true 2> /dev/null
+  then
+    echo "ratio-to-prev [Skipped not supported]"
+    return
+  fi
+  if ! perf record -o /dev/null -e "instructions, cycles/period=100000,ratio-to-prev=0.5/" \
+     true |& grep -q 'Invalid use of ratio-to-prev term without preceding element in group'
+  then
+    echo "ratio-to-prev test [Failed elements must be in same group]"
+    err=1
+    return
+  fi
+  if ! perf record -o /dev/null -e "{instructions,dummy,cycles/period=100000,ratio-to-prev=0.5/}" \
+     true |& grep -q 'must have same PMU'
+  then
+    echo "ratio-to-prev test [Failed elements must have same PMU]"
+    err=1
+    return
+  fi
+  if ! perf record -o /dev/null -e "{instructions,cycles/ratio-to-prev=0.5/}" \
+     true |& grep -q 'Event period term or count (-c) must be set when using ratio-to-prev term.'
+  then
+    echo "ratio-to-prev test [Failed period must be set]"
+    err=1
+    return
+  fi
+  if ! perf record -o /dev/null -e "{cycles/ratio-to-prev=0.5/}" \
+     true |& grep -q 'Invalid use of ratio-to-prev term without preceding element in group'
+  then
+    echo "ratio-to-prev test [Failed need 2+ events]"
+    err=1
+    return
+  fi
+  echo "Basic ratio-to-prev record test [Success]"
+}
+
 # raise the limit of file descriptors to minimum
 if [[ $default_fd_limit -lt $min_fd_limit ]]; then
        ulimit -Sn $min_fd_limit
@@ -404,6 +443,7 @@ test_leader_sampling
 test_topdown_leader_sampling
 test_precise_max
 test_callgraph
+test_ratio_to_prev
 
 # restore the default value
 ulimit -Sn $default_fd_limit
-- 
2.50.1

Re: [Patch v3 0/2] perf record: ratio-to-prev event term for auto counter reload

[Arnaldo Carvalho de Melo]

On Thu, Oct 02, 2025 at 06:43:04PM -0500, thomas.falcon@intel.com wrote:
> The goal is to limit event sampling to cases when the branch miss rate
> exceeds 20%. If the branch instructions sample period is exceeded
> first, both events are reloaded.  If branch misses exceed their
> threshold first, only the second counter is reloaded, and a sample is
> taken.
 
> To simplify this, provide a new “ratio-to-prev” event term
> that works alongside the period event option or -c option.
> This would allow users to specify the desired relative rate
> between events as a ratio, making configuration more intuitive.
 
> With this enhancement, the equivalent command would be:
> 
> perf record -e "{cpu_atom/branch-misses/ppu,\
> cpu_atom/branch-instructions,period=1000000,ratio_to_prev=5/u}" \
> -- ./mispredict
> or
> perf record -e "{cpu_atom/branch-misses/ppu,\
> cpu_atom/branch-instructions,ratio-to-prev=5/u}" -c 1000000 \
> -- ./mispredict
> [1] https://lore.kernel.org/lkml/20250327195217.2683619-1-kan.liang@linux.intel.com/
> v3: rebase to current perf-tools-next

Thanks, applied to perf-tools-next,

- Arnaldo
 
> v2: (changes below suggested by Ian Rogers):

Re: [Patch v3 0/2] perf record: ratio-to-prev event term for auto counter reload

[Falcon, Thomas]

On Fri, 2025-10-03 at 16:27 -0300, Arnaldo Carvalho de Melo wrote:
> On Thu, Oct 02, 2025 at 06:43:04PM -0500,
> thomas.falcon@intel.com wrote:
> > The goal is to limit event sampling to cases when the branch miss
> > rate
> > exceeds 20%. If the branch instructions sample period is exceeded
> > first, both events are reloaded.  If branch misses exceed their
> > threshold first, only the second counter is reloaded, and a sample
> > is
> > taken.
>  
> > To simplify this, provide a new “ratio-to-prev” event term
> > that works alongside the period event option or -c option.
> > This would allow users to specify the desired relative rate
> > between events as a ratio, making configuration more intuitive.
>  
> > With this enhancement, the equivalent command would be:
> > 
> > perf record -e "{cpu_atom/branch-misses/ppu,\
> > cpu_atom/branch-instructions,period=1000000,ratio_to_prev=5/u}" \
> > -- ./mispredict
> > or
> > perf record -e "{cpu_atom/branch-misses/ppu,\
> > cpu_atom/branch-instructions,ratio-to-prev=5/u}" -c 1000000 \
> > -- ./mispredict
> > [1]
> > https://lore.kernel.org/lkml/20250327195217.2683619-1-kan.liang@linux.intel.com/
> > v3: rebase to current perf-tools-next
> 
> Thanks, applied to perf-tools-next,
> 
> - Arnaldo
>  

Thank you and thanks to Ian and everyone else that took their time to
review.

Thanks,
Tom

> > v2: (changes below suggested by Ian Rogers):
>