[PATCH v2 03/18] perf test: Add a workload that forces context switches

[James Clark]

This workload launches two processes that block when reading and writing
to each other forcing the other process to be scheduled for each
read/write pair.

Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
---
 tools/perf/Documentation/perf-test.txt           |  7 +-
 tools/perf/tests/builtin-test.c                  |  1 +
 tools/perf/tests/tests.h                         |  1 +
 tools/perf/tests/workloads/Build                 |  1 +
 tools/perf/tests/workloads/context_switch_loop.c | 95 ++++++++++++++++++++++++
 5 files changed, 102 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-test.txt b/tools/perf/Documentation/perf-test.txt
index 1faf30d4a7be..9c0d7ac2bc64 100644
--- a/tools/perf/Documentation/perf-test.txt
+++ b/tools/perf/Documentation/perf-test.txt
@@ -55,15 +55,16 @@ OPTIONS
 
 -w::
 --workload=::
-	Run a built-in workload, to list them use '--list-workloads', current ones include:
-	noploop, thloop, leafloop, sqrtloop, brstack, datasym and landlock.
+	Run a built-in workload, to list them use '--list-workloads', current
+	ones include: noploop, thloop, leafloop, sqrtloop, brstack, datasym,
+	context_switch_loop and landlock.
 
 	Used with the shell script regression tests.
 
 	Some accept an extra parameter:
 
 		seconds: leafloop, noploop, sqrtloop, thloop
-		nrloops: brstack
+		nrloops: brstack, context_switch_loop
 
 	The datasym and landlock workloads don't accept any.
 
diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
index d5df3efdce3b..1057ee836c30 100644
--- a/tools/perf/tests/builtin-test.c
+++ b/tools/perf/tests/builtin-test.c
@@ -156,6 +156,7 @@ static struct test_workload *workloads[] = {
 	&workload__landlock,
 	&workload__traploop,
 	&workload__inlineloop,
+	&workload__context_switch_loop,
 
 #ifdef HAVE_RUST_SUPPORT
 	&workload__code_with_type,
diff --git a/tools/perf/tests/tests.h b/tools/perf/tests/tests.h
index ee00518bf36f..79f50bacfc94 100644
--- a/tools/perf/tests/tests.h
+++ b/tools/perf/tests/tests.h
@@ -242,6 +242,7 @@ DECLARE_WORKLOAD(datasym);
 DECLARE_WORKLOAD(landlock);
 DECLARE_WORKLOAD(traploop);
 DECLARE_WORKLOAD(inlineloop);
+DECLARE_WORKLOAD(context_switch_loop);
 
 #ifdef HAVE_RUST_SUPPORT
 DECLARE_WORKLOAD(code_with_type);
diff --git a/tools/perf/tests/workloads/Build b/tools/perf/tests/workloads/Build
index 2ef97f7affce..3bda6da04a35 100644
--- a/tools/perf/tests/workloads/Build
+++ b/tools/perf/tests/workloads/Build
@@ -9,6 +9,7 @@ perf-test-y += datasym.o
 perf-test-y += landlock.o
 perf-test-y += traploop.o
 perf-test-y += inlineloop.o
+perf-test-y += context_switch_loop.o
 
 ifeq ($(CONFIG_RUST_SUPPORT),y)
     perf-test-y += code_with_type.o
diff --git a/tools/perf/tests/workloads/context_switch_loop.c b/tools/perf/tests/workloads/context_switch_loop.c
new file mode 100644
index 000000000000..73bfcaeff5b0
--- /dev/null
+++ b/tools/perf/tests/workloads/context_switch_loop.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/compiler.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../tests.h"
+
+static int loops = 100;
+static char buf;
+int context_switch_loop_work = 1234;
+
+#define write_block(fd) \
+	do { \
+		if (write(fd, &buf, 1) <= 0) \
+			exit(1); \
+	} while (0)
+
+#define read_block(fd) \
+	do { \
+		if (read(fd, &buf, 1) <= 0) \
+			exit(1); \
+	} while (0)
+
+/* Not static to avoid LTO clobbering the function name */
+void context_switch_loop_proc1(int in_fd, int out_fd);
+noinline void context_switch_loop_proc1(int in_fd, int out_fd)
+{
+	for (int i = 0; i < loops; i++) {
+		read_block(in_fd);
+		context_switch_loop_work += i * 3;
+		write_block(out_fd);
+	}
+}
+
+void context_switch_loop_proc2(int in_fd, int out_fd);
+noinline void context_switch_loop_proc2(int in_fd, int out_fd)
+{
+	for (int i = 0; i < loops; i++) {
+		write_block(out_fd);
+		context_switch_loop_work += i * 7;
+		read_block(in_fd);
+	}
+}
+
+/*
+ * Launches two processes that take turns to execute a multiplication N times
+ */
+static int context_switch_loop(int argc, const char **argv)
+{
+	int a_to_b[2], b_to_a[2];
+	pid_t proc1_pid;
+	int status;
+
+	if (argc > 0) {
+		loops = atoi(argv[0]);
+		if (loops < 0) {
+			fprintf(stderr, "Invalid number of loops: %s\n", argv[0]);
+			return 1;
+		}
+	}
+
+	if (pipe(a_to_b) || pipe(b_to_a)) {
+		perror("Pipe error");
+		return 1;
+	}
+
+	proc1_pid = fork();
+	if (proc1_pid < 0) {
+		perror("Fork error");
+		return 1;
+	}
+
+	if (!proc1_pid) {
+		close(a_to_b[0]);
+		close(b_to_a[1]);
+		prctl(PR_SET_NAME, "proc1", 0, 0, 0);
+		context_switch_loop_proc1(b_to_a[0], a_to_b[1]);
+		exit(0);
+	}
+
+	prctl(PR_SET_NAME, "proc2", 0, 0, 0);
+	context_switch_loop_proc2(a_to_b[0], b_to_a[1]);
+
+	if (waitpid(proc1_pid, &status, 0) != proc1_pid || !WIFEXITED(status) ||
+	    WEXITSTATUS(status))
+		return 1;
+
+	return 0;
+}
+
+DEFINE_WORKLOAD(context_switch_loop);

-- 
2.34.1