linux-kernel - [PATCH] perf/bench: Fix perf bench syscall XXXX loop count

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Message-ID: <20250304092349.2618082-1-tmricht@linux.ibm.com>
Date: Tue,  4 Mar 2025 10:23:49 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org, namhyung@...nel.org,
        yangtiezhu@...ngson.cn
Cc: agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com, Thomas Richter <tmricht@...ux.ibm.com>
Subject: [PATCH] perf/bench: Fix perf bench syscall XXXX loop count

Command 'perf bench syscall fork -l 100000' offers option
-l to run for a specified number of iterations. However this
option is not always observed. The number is silently limited to
10000 iterations as can be seen:

Output before:
 # perf bench syscall fork -l 100000
 # Running 'syscall/fork' benchmark:
 # Executed 10,000 fork() calls
     Total time: 23.388 [sec]

    2338.809800 usecs/op
            427 ops/sec
 #

When explicitly specified with option -l or --loops, also observe
higher number of iterations:

Output after:
 # perf bench syscall fork -l 100000
 # Running 'syscall/fork' benchmark:
 # Executed 100,000 fork() calls
     Total time: 716.982 [sec]

    7169.829510 usecs/op
            139 ops/sec
 #

This patch fixes the issue for basic execve fork and getpgid.

Fixes: ece7f7c0507c ("perf bench syscall: Add fork syscall benchmark")
Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/perf/bench/syscall.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/tools/perf/bench/syscall.c b/tools/perf/bench/syscall.c
index ea4dfc07cbd6..e7dc216f717f 100644
--- a/tools/perf/bench/syscall.c
+++ b/tools/perf/bench/syscall.c
@@ -22,8 +22,7 @@
 #define __NR_fork -1
 #endif
 
-#define LOOPS_DEFAULT 10000000
-static	int loops = LOOPS_DEFAULT;
+static	int loops;
 
 static const struct option options[] = {
 	OPT_INTEGER('l', "loop",	&loops,		"Specify number of loops"),
@@ -80,6 +79,18 @@ static int bench_syscall_common(int argc, const char **argv, int syscall)
 	const char *name = NULL;
 	int i;
 
+	switch (syscall) {
+	case __NR_fork:
+	case __NR_execve:
+		/* Limit default loop to 10000 times to save time */
+		loops = 10000;
+		break;
+	default:
+		loops = 10000000;
+		break;
+	}
+
+	/* Options -l and --loops override default above */
 	argc = parse_options(argc, argv, options, bench_syscall_usage, 0);
 
 	gettimeofday(&start, NULL);
@@ -94,16 +105,9 @@ static int bench_syscall_common(int argc, const char **argv, int syscall)
 			break;
 		case __NR_fork:
 			test_fork();
-			/* Only loop 10000 times to save time */
-			if (i == 10000)
-				loops = 10000;
 			break;
 		case __NR_execve:
 			test_execve();
-			/* Only loop 10000 times to save time */
-			if (i == 10000)
-				loops = 10000;
-			break;
 		default:
 			break;
 		}
-- 
2.47.0