perf tools: sched-pipe bench: add (-n) nonblocking benchmark

The -n mode will benchmark pipes in a non-blocking mode using
epoll_wait.

This specific mode was added to demonstrate the broken sync nature
of epoll: https://lore.kernel.org/lkml/20240426-zupfen-jahrzehnt-5be786bcdf04@brauner

Signed-off-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20241016190009.866615-1-bgeffon@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

diff --git a/tools/perf/bench/sched-pipe.c b/tools/perf/bench/sched-pipe.c
index 3af6d3c55aba19865c33861ff6a4d0e12cb08b61..e2562677df964090fa37228c1b0115b1ec50e4d5 100644 (file)
--- a/tools/perf/bench/sched-pipe.c
+++ b/tools/perf/bench/sched-pipe.c
@@ -23,6 +23,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <assert.h>
+#include <sys/epoll.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/syscall.h>
@@ -34,6 +35,8 @@ struct thread_data {
        int                     nr;
        int                     pipe_read;
        int                     pipe_write;
+       struct epoll_event      epoll_ev;
+       int                     epoll_fd;
        bool                    cgroup_failed;
        pthread_t               pthread;
 };
@@ -44,6 +47,7 @@ static        int                     loops = LOOPS_DEFAULT;
 /* Use processes by default: */
 static bool                    threaded;
 
+static bool                    nonblocking;
 static char                    *cgrp_names[2];
 static struct cgroup           *cgrps[2];
 
@@ -81,6 +85,7 @@ out:
 }
 
 static const struct option options[] = {
+       OPT_BOOLEAN('n', "nonblocking", &nonblocking,   "Use non-blocking operations"),
        OPT_INTEGER('l', "loop",        &loops,         "Specify number of loops"),
        OPT_BOOLEAN('T', "threaded",    &threaded,      "Specify threads/process based task setup"),
        OPT_CALLBACK('G', "cgroups", NULL, "SEND,RECV",
@@ -165,11 +170,25 @@ static void exit_cgroup(int nr)
        free(cgrp_names[nr]);
 }
 
+static inline int read_pipe(struct thread_data *td)
+{
+       int ret, m;
+retry:
+       if (nonblocking) {
+               ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);
+               if (ret < 0)
+                       return ret;
+       }
+       ret = read(td->pipe_read, &m, sizeof(int));
+       if (nonblocking && ret < 0 && errno == EWOULDBLOCK)
+               goto retry;
+       return ret;
+}
+
 static void *worker_thread(void *__tdata)
 {
        struct thread_data *td = __tdata;
-       int m = 0, i;
-       int ret;
+       int i, ret, m = 0;
 
        ret = enter_cgroup(td->nr);
        if (ret < 0) {
@@ -177,16 +196,23 @@ static void *worker_thread(void *__tdata)
                return NULL;
        }
 
+       if (nonblocking) {
+               td->epoll_ev.events = EPOLLIN;
+               td->epoll_fd = epoll_create(1);
+               BUG_ON(td->epoll_fd < 0);
+               BUG_ON(epoll_ctl(td->epoll_fd, EPOLL_CTL_ADD, td->pipe_read, &td->epoll_ev) < 0);
+       }
+
        for (i = 0; i < loops; i++) {
                if (!td->nr) {
-                       ret = read(td->pipe_read, &m, sizeof(int));
+                       ret = read_pipe(td);
                        BUG_ON(ret != sizeof(int));
                        ret = write(td->pipe_write, &m, sizeof(int));
                        BUG_ON(ret != sizeof(int));
                } else {
                        ret = write(td->pipe_write, &m, sizeof(int));
                        BUG_ON(ret != sizeof(int));
-                       ret = read(td->pipe_read, &m, sizeof(int));
+                       ret = read_pipe(td);
                        BUG_ON(ret != sizeof(int));
                }
        }
@@ -209,13 +235,16 @@ int bench_sched_pipe(int argc, const char **argv)
         * discarding returned value of read(), write()
         * causes error in building environment for perf
         */
-       int __maybe_unused ret, wait_stat;
+       int __maybe_unused ret, wait_stat, flags = 0;
        pid_t pid, retpid __maybe_unused;
 
        argc = parse_options(argc, argv, options, bench_sched_pipe_usage, 0);
 
-       BUG_ON(pipe(pipe_1));
-       BUG_ON(pipe(pipe_2));
+       if (nonblocking)
+               flags |= O_NONBLOCK;
+
+       BUG_ON(pipe2(pipe_1, flags));
+       BUG_ON(pipe2(pipe_2, flags));
 
        gettimeofday(&start, NULL);