linux-kernel - [PATCH v2] perf sched replay: Fix -r/--repeat command line option for infinity

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Date: Fri, 21 Jun 2024 22:49:09 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        James Clark <james.clark@....com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
        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>, acme@...hat.com,
        Chen Yu <yu.c.chen@...el.com>, Fernand Sieber <sieberf@...zon.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: [PATCH v2] perf sched replay: Fix -r/--repeat command line option for infinity

Currently, the -r/--repeat option accepts values from 0 and complains
for -1. The help section specifies:
-r, --repeat <n>      repeat the workload replay N times (-1: infinite)

The -r -1 option raises an error because replay_repeat is defined as
an unsigned int.

In the current implementation, the workload is repeated n times when
-r <n> is used, except when n is 0.

When -r is set to 0, the workload is also repeated once. This happens
because when -r=0, the run_one_test function is not called. (Note that
mutex unlocking, which is essential for child threads spawned to emulate
the workload, happens in run_one_test.) However, mutex unlocking is
still performed in the destroy_tasks function. Thus, -r=0 results in the
workload running once coincidentally.

To clarify and maintain the existing logic for -r >= 1 (which runs the
workload the specified number of times) and to fix the issue with infinite
runs, make -r=0 perform an infinite run.

Signed-off-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Reviewed-by: James Clark <james.clark@....com>

---
Changes in v2:
- Kept the existing 'for' loop and added a condition for infinite
  looping. (James Clark)
- This change also ensures that integer overflow doesn't occur when
  'replay_repeat' is zero.
- Add Reviewed-by tag from James Clark.
- Rebase against perf-tools-next commit 788c5160526a ("perf vendor
  events: Add westmereex counter information")
- Link to v1: https://lore.kernel.org/all/20240618112907.15131-1-vineethr@linux.ibm.com/

 tools/perf/Documentation/perf-sched.txt |  7 +++++++
 tools/perf/builtin-sched.c              | 11 ++++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-sched.txt b/tools/perf/Documentation/perf-sched.txt
index a216d2991b19..f1be8f0b249e 100644
--- a/tools/perf/Documentation/perf-sched.txt
+++ b/tools/perf/Documentation/perf-sched.txt
@@ -202,6 +202,13 @@ OPTIONS for 'perf sched timehist'
 --state::
 	Show task state when it switched out.
 
+OPTIONS for 'perf sched replay'
+------------------------------
+
+-r::
+--repeat <n>::
+	repeat the workload n times (0: infinite). Default is 10.
+
 SEE ALSO
 --------
 linkperf:perf-record[1]
diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 8cdf18139a7e..51b3dea404bc 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -3383,8 +3383,13 @@ static int perf_sched__replay(struct perf_sched *sched)
 	sched->thread_funcs_exit = false;
 	create_tasks(sched);
 	printf("------------------------------------------------------------\n");
-	for (i = 0; i < sched->replay_repeat; i++)
-		run_one_test(sched);
+	if (sched->replay_repeat == 0) {
+		while (1)
+			run_one_test(sched);
+	} else {
+		for (i = 0; i < sched->replay_repeat; i++)
+			run_one_test(sched);
+	}
 
 	sched->thread_funcs_exit = true;
 	destroy_tasks(sched);
@@ -3548,7 +3553,7 @@ int cmd_sched(int argc, const char **argv)
 	};
 	const struct option replay_options[] = {
 	OPT_UINTEGER('r', "repeat", &sched.replay_repeat,
-		     "repeat the workload replay N times (-1: infinite)"),
+		     "repeat the workload replay N times (0: infinite)"),
 	OPT_PARENT(sched_options)
 	};
 	const struct option map_options[] = {
-- 
2.31.1