[PATCH] perf stat: Add event-interval-print option

[Aaron Lindsay]

This allows for printing counts at regular intervals based on <n>
instances of an arbitrary event (currently the first event provided).

This can be useful when comparing `perf stat` runs of fixed-work
workloads. For instance, you may want to compare interval-by-interval
stats between two runs based on instruction count rather than time
intervals to ensure the same sections of the userspace component of code
are aligned when comparing them (which wouldn't necessarily be the case
if the kernel was misbehaving in only one of the compared runs).

Signed-off-by: Aaron Lindsay <alindsay@xxxxxxxxxxxxxx>
Tested-by: Digant Desai <digantd@xxxxxxxxxxxxxx>
---
 tools/perf/builtin-stat.c | 114 ++++++++++++++++++++++++++++++++++++++++++----
 tools/perf/util/evsel.h   |   1 +
 tools/perf/util/stat.h    |   1 +
 3 files changed, 107 insertions(+), 9 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 48ac53b..e400cd3 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -71,7 +71,9 @@
 #include <api/fs/fs.h>
 #include <errno.h>
 #include <signal.h>
+#include <poll.h>
 #include <stdlib.h>
+#include <sys/mman.h>
 #include <sys/prctl.h>
 #include <inttypes.h>
 #include <locale.h>
@@ -224,7 +226,8 @@ static int create_perf_stat_counter(struct perf_evsel *evsel)
 	 * Some events get initialized with sample_(period/type) set,
 	 * like tracepoints. Clear it up for counting.
 	 */
-	attr->sample_period = 0;
+	if (!evsel->event_interval)
+		attr->sample_period = 0;
 
 	/*
 	 * But set sample_type to PERF_SAMPLE_IDENTIFIER, which should be harmless
@@ -562,6 +565,7 @@ static int store_counter_ids(struct perf_evsel *counter)
 static int __run_perf_stat(int argc, const char **argv)
 {
 	int interval = stat_config.interval;
+	int event_interval = stat_config.event_interval;
 	char msg[BUFSIZ];
 	unsigned long long t0, t1;
 	struct perf_evsel *counter;
@@ -571,6 +575,9 @@ static int __run_perf_stat(int argc, const char **argv)
 	const bool forks = (argc > 0);
 	bool is_pipe = STAT_RECORD ? perf_stat.file.is_pipe : false;
 	struct perf_evsel_config_term *err_term;
+	bool first_counter = true;
+
+	struct pollfd interval_pollfd = {.fd = 0, .events = POLLIN};
 
 	if (interval) {
 		ts.tv_sec  = interval / USEC_PER_MSEC;
@@ -594,6 +601,32 @@ static int __run_perf_stat(int argc, const char **argv)
 
 	evlist__for_each_entry(evsel_list, counter) {
 try_again:
+		if (first_counter && event_interval) {
+			/*
+			 * Setup this counter as an event interval by pinning
+			 * it, setting it to sample based on the user-specified
+			 * period, and to return from polling on expiration
+			 * (i.e. when any data is written to the buffer)
+			 */
+			int nthreads = thread_map__nr(evsel_list->threads);
+			int ncpus = perf_evsel__nr_cpus(counter);
+
+			if (nthreads > 1 || ncpus > 1) {
+				perror("Failed to setup event-interval-print "
+				       "because the event has more than one "
+				       "CPU or thread.");
+				return -1;
+			}
+
+			counter->attr.pinned = 1;
+			counter->attr.watermark = 1;
+			counter->attr.wakeup_watermark = 1;
+			counter->attr.sample_period = event_interval;
+			counter->attr.freq = 0;
+			counter->event_interval = true;
+
+			pr_debug2("Polling on %s\n", perf_evsel__name(counter));
+		}
 		if (create_perf_stat_counter(counter) < 0) {
 			/*
 			 * PPC returns ENXIO for HW counters until 2.6.37
@@ -633,6 +666,33 @@ static int __run_perf_stat(int argc, const char **argv)
 
 		if (STAT_RECORD && store_counter_ids(counter))
 			return -1;
+
+		if (first_counter && event_interval) {
+			void *m;
+
+			interval_pollfd.fd =
+				*(int *)xyarray__entry(counter->fd, 0, 0);
+
+			/*
+			 * Do not set PROT_WRITE since the kernel will stop
+			 * writing to the mmap buffer when it fills if
+			 * data_tail is not set. Map 2 pages since the kernel
+			 * requires the first for metadata.
+			 */
+			m = mmap(NULL, 2 * getpagesize(), PROT_READ, MAP_SHARED,
+					interval_pollfd.fd, 0);
+			if (m == (void *) -1) {
+				perror("Failed to mmap print-event-interval "
+				       "fd");
+				return -1;
+			}
+		}
+
+		first_counter = false;
+	}
+	if (event_interval && !interval_pollfd.fd) {
+		perror("Failed to initialize print-event-interval fd");
+		return -1;
 	}
 
 	if (perf_evlist__apply_filters(evsel_list, &counter)) {
@@ -677,7 +737,18 @@ static int __run_perf_stat(int argc, const char **argv)
 		perf_evlist__start_workload(evsel_list);
 		enable_counters();
 
-		if (interval) {
+		if (event_interval) {
+			while (!waitpid(child_pid, &status, WNOHANG)) {
+				/*
+				 * Wait for the event to expire for at most 1
+				 * second
+				 */
+				if (poll(&interval_pollfd, 1, 1000) > 0) {
+					if (interval_pollfd.revents & (POLLIN))
+						process_interval();
+				}
+			}
+		} else if (interval) {
 			while (!waitpid(child_pid, &status, WNOHANG)) {
 				nanosleep(&ts, NULL);
 				process_interval();
@@ -696,9 +767,20 @@ static int __run_perf_stat(int argc, const char **argv)
 	} else {
 		enable_counters();
 		while (!done) {
-			nanosleep(&ts, NULL);
-			if (interval)
-				process_interval();
+			if (event_interval) {
+				/*
+				 * Wait for the event to expire for at most 1
+				 * second
+				 */
+				if (poll(&interval_pollfd, 1, 1000) > 0) {
+					if (interval_pollfd.revents & (POLLIN))
+						process_interval();
+				}
+			} else {
+				nanosleep(&ts, NULL);
+				if (interval)
+					process_interval();
+			}
 		}
 	}
 
@@ -1614,7 +1696,7 @@ static void print_footer(void)
 
 static void print_counters(struct timespec *ts, int argc, const char **argv)
 {
-	int interval = stat_config.interval;
+	int interval = stat_config.interval || stat_config.event_interval;
 	struct perf_evsel *counter;
 	char buf[64], *prefix = NULL;
 
@@ -1781,6 +1863,8 @@ static int enable_metric_only(const struct option *opt __maybe_unused,
 			"command to run after to the measured command"),
 	OPT_UINTEGER('I', "interval-print", &stat_config.interval,
 		    "print counts at regular interval in ms (>= 10)"),
+	OPT_UINTEGER('E', "event-interval-print", &stat_config.event_interval,
+		    "print counts every <n> of the first event specified"),
 	OPT_SET_UINT(0, "per-socket", &stat_config.aggr_mode,
 		     "aggregate counts per processor socket", AGGR_SOCKET),
 	OPT_SET_UINT(0, "per-core", &stat_config.aggr_mode,
@@ -2546,7 +2630,7 @@ int cmd_stat(int argc, const char **argv)
 	int status = -EINVAL, run_idx;
 	const char *mode;
 	FILE *output = stderr;
-	unsigned int interval;
+	unsigned int interval, event_interval;
 	const char * const stat_subcommands[] = { "record", "report" };
 
 	setlocale(LC_ALL, "");
@@ -2577,6 +2661,7 @@ int cmd_stat(int argc, const char **argv)
 		return __cmd_report(argc, argv);
 
 	interval = stat_config.interval;
+	event_interval = stat_config.event_interval;
 
 	/*
 	 * For record command the -o is already taken care of.
@@ -2704,6 +2789,17 @@ int cmd_stat(int argc, const char **argv)
 	if (stat_config.aggr_mode == AGGR_THREAD)
 		thread_map__read_comms(evsel_list->threads);
 
+	if (interval && event_interval) {
+		pr_err("interval-print and event-interval-print options "
+			"cannot be used together\n");
+		goto out;
+	}
+
+	if (event_interval && !no_inherit) {
+		pr_err("The event-interval-print option requires no-inherit\n");
+		goto out;
+	}
+
 	if (interval && interval < 100) {
 		if (interval < 10) {
 			pr_err("print interval must be >= 10ms\n");
@@ -2715,7 +2811,7 @@ int cmd_stat(int argc, const char **argv)
 				   "Please proceed with caution.\n");
 	}
 
-	if (perf_evlist__alloc_stats(evsel_list, interval))
+	if (perf_evlist__alloc_stats(evsel_list, interval || event_interval))
 		goto out;
 
 	if (perf_stat_init_aggr_mode())
@@ -2747,7 +2843,7 @@ int cmd_stat(int argc, const char **argv)
 		}
 	}
 
-	if (!forever && status != -1 && !interval)
+	if (!forever && status != -1 && !interval && !event_interval)
 		print_counters(NULL, argc, argv);
 
 	if (STAT_RECORD) {
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index d101695..44a65e6 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -121,6 +121,7 @@ struct perf_evsel {
 	bool			per_pkg;
 	bool			precise_max;
 	bool			ignore_missing_thread;
+	bool			event_interval;
 	/* parse modifier helper */
 	int			exclude_GH;
 	int			nr_members;
diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
index 7522bf1..db4dda4 100644
--- a/tools/perf/util/stat.h
+++ b/tools/perf/util/stat.h
@@ -46,6 +46,7 @@ struct perf_stat_config {
 	bool		scale;
 	FILE		*output;
 	unsigned int	interval;
+	unsigned int	event_interval;
 };
 
 void update_stats(struct stats *stats, u64 val);
-- 
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