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perf bench: Add --write-size option to sched pipe

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The default ping-pong uses sizeof(int) (4 bytes) per iteration, which
exercises only the pipe-buffer merge path and keeps allocation entirely
out of the picture. That makes the bench a useful scheduler / context-
switch latency probe but unable to surface anything from the pipe
page-allocation hot path.

Add a -s/--write-size option that sets the bytes written and read per
ping-pong iteration. The buffer is allocated for each side via struct
thread_data and replaces the on-stack int previously used. The default
remains sizeof(int) so existing invocations are unchanged.

With --write-size set above PAGE_SIZE the bench drives anon_pipe_write()
through alloc_page() (or the bulk pre-alloc, if the relevant patch is
applied), which is what we want when measuring pipe locking and page
allocation work.

The bench is a ping-pong: both sides call write() before read(), so a
single write_size payload must fit entirely in the pipe buffer or both
sides deadlock waiting for the other to drain.

Resize the pipe via F_SETPIPE_SZ to match write_size (skipped at the
sizeof(int) default), and error out cleanly when the request exceeds
/proc/sys/fs/pipe-max-size.

Committer testing:

  ⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe
  # Running 'sched/pipe' benchmark:
  # Executed 1000000 pipe operations between two processes

     Total time: 0.915 [sec]

       0.915493 usecs/op
        1092307 ops/sec
  ⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 1024
  # Running 'sched/pipe' benchmark:
  # Executed 1000000 pipe operations between two processes

     Total time: 0.891 [sec]

       0.891915 usecs/op
        1121183 ops/sec
  ⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 4096
  # Running 'sched/pipe' benchmark:
  # Executed 1000000 pipe operations between two processes

     Total time: 1.366 [sec]

       1.366073 usecs/op
         732025 ops/sec
  ⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe --write-size 4096
  # Running 'sched/pipe' benchmark:
  fcntl(4, F_SETPIPE_SZ, 4096)            = 4096
  fcntl(6, F_SETPIPE_SZ, 4096)            = 4096
  ^Cstrace: Process 17840 detached

  ⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe --write-size 1024
  # Running 'sched/pipe' benchmark:
  fcntl(4, F_SETPIPE_SZ, 1024)            = 4096
  fcntl(6, F_SETPIPE_SZ, 1024)            = 4096
  ^Cstrace: Process 17845 detached

  ⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe
  # Running 'sched/pipe' benchmark:
  ^Cstrace: Process 17851 detached

  ⬢ [acme@toolbx perf-tools-next]$
  ⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 1048577
  # Running 'sched/pipe' benchmark:
  --write-size 1048577 exceeds /proc/sys/fs/pipe-max-size
  ⬢ [acme@toolbx perf-tools-next]$ cat /proc/sys/fs/pipe-max-size
  1048576
  ⬢ [acme@toolbx perf-tools-next]$
  acme@number:~/git/perf-tools-next$

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Breno Leitao 2026-06-03 03:35:07 -07:00 committed by Arnaldo Carvalho de Melo
parent 044462f6f6
commit b52ba22c70
1 changed files with 116 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

129
tools/perf/bench/sched-pipe.c
View File

@ -22,7 +22,9 @@
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <assert.h>
#include <poll.h>
#include <sys/epoll.h>
#include <sys/time.h>
#include <sys/types.h>
@ -39,6 +41,7 @@ struct thread_data {
int epoll_fd;
bool cgroup_failed;
pthread_t pthread;
char *buf;
};
#define LOOPS_DEFAULT 1000000
@ -48,6 +51,7 @@ static int loops = LOOPS_DEFAULT;
static bool threaded;
static bool nonblocking;
static unsigned int write_size = sizeof(int);
static char *cgrp_names[2];
static struct cgroup *cgrps[2];
@ -88,6 +92,8 @@ 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_UINTEGER('s', "write-size", &write_size,
"Bytes per ping-pong write (default 4-bytes). Use larger values to exercise the pipe page-allocation path."),
OPT_CALLBACK('G', "cgroups", NULL, "SEND,RECV",
"Put sender and receivers in given cgroups",
parse_two_cgroups),
@ -170,25 +176,77 @@ static void exit_cgroup(int nr)
free(cgrp_names[nr]);
}
/* Sleep until @fd is writable, so we don't busy-spin on EWOULDBLOCK. */
static inline void wait_writable(int fd)
{
struct pollfd pfd = {
.fd = fd,
.events = POLLOUT,
};
poll(&pfd, 1, -1);
}
/*
* Loop on short read()/write(): the kernel may return fewer bytes than
* requested, retry on EINTR, and in non-blocking mode wait via poll()
* when the writer transiently hits EWOULDBLOCK while the peer is still
* draining a full pipe (capacity is sized to write_size).
*/
static inline int write_pipe(struct thread_data *td)
{
unsigned int done = 0;
int ret;
while (done < write_size) {
ret = write(td->pipe_write, td->buf + done, write_size - done);
if (ret < 0) {
if (errno == EINTR)
continue;
if (nonblocking && errno == EWOULDBLOCK) {
wait_writable(td->pipe_write);
continue;
}
return ret;
}
done += ret;
}
return done;
}
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)
unsigned int done = 0;
int ret;
while (done < write_size) {
if (nonblocking) {
ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);
if (ret < 0) {
if (errno == EINTR)
continue;
return ret;
}
}
ret = read(td->pipe_read, td->buf + done, write_size - done);
if (ret < 0) {
if (errno == EINTR)
continue;
if (nonblocking && errno == EWOULDBLOCK)
continue;
return ret;
}
if (ret == 0)
return done;
done += ret;
}
ret = read(td->pipe_read, &m, sizeof(int));
if (nonblocking && ret < 0 && errno == EWOULDBLOCK)
goto retry;
return ret;
return done;
}
static void *worker_thread(void *__tdata)
{
struct thread_data *td = __tdata;
int i, ret, m = 0;
int i, ret;
ret = enter_cgroup(td->nr);
if (ret < 0) {
@ -204,15 +262,38 @@ static void *worker_thread(void *__tdata)
}
for (i = 0; i < loops; i++) {
ret = write(td->pipe_write, &m, sizeof(int));
BUG_ON(ret != sizeof(int));
ret = write_pipe(td);
BUG_ON(ret != (int)write_size);
ret = read_pipe(td);
BUG_ON(ret != sizeof(int));
BUG_ON(ret != (int)write_size);
}
return NULL;
}
/*
* On a custom write_size, resize the pipes so a single payload fits.
*/
static int resize_pipes(int wfd1, int wfd2)
{
int r1, r2;
if (write_size <= sizeof(int))
return 0;
r1 = fcntl(wfd1, F_SETPIPE_SZ, write_size);
r2 = fcntl(wfd2, F_SETPIPE_SZ, write_size);
if (r1 < 0 || r2 < 0 ||
(unsigned int)r1 < write_size ||
(unsigned int)r2 < write_size) {
fprintf(stderr,
"--write-size %u exceeds /proc/sys/fs/pipe-max-size\n",
write_size);
return -1;
}
return 0;
}
int bench_sched_pipe(int argc, const char **argv)
{
struct thread_data threads[2] = {};
@ -233,12 +314,31 @@ int bench_sched_pipe(int argc, const char **argv)
argc = parse_options(argc, argv, options, bench_sched_pipe_usage, 0);
/*
* The error paths below return early without closing the pipes or
* freeing the cgroup state. That is fine: bench_sched_pipe() runs
* once and the process exits right after it returns, so these are
* not real leaks.
*/
if (write_size == 0 || write_size > INT_MAX) {
fprintf(stderr, "--write-size must be in 1..%d\n", INT_MAX);
return -1;
}
if (nonblocking)
flags |= O_NONBLOCK;
BUG_ON(pipe2(pipe_1, flags));
BUG_ON(pipe2(pipe_2, flags));
if (resize_pipes(pipe_1[1], pipe_2[1]) < 0)
return -1;
for (t = 0; t < nr_threads; t++) {
threads[t].buf = calloc(1, write_size);
BUG_ON(!threads[t].buf);
}
gettimeofday(&start, NULL);
for (t = 0; t < nr_threads; t++) {
@ -287,6 +387,9 @@ int bench_sched_pipe(int argc, const char **argv)
gettimeofday(&stop, NULL);
timersub(&stop, &start, &diff);
for (t = 0; t < nr_threads; t++)
free(threads[t].buf);
exit_cgroup(0);
exit_cgroup(1);