Re: [PATCH] perf record: Use an eventfd to wakeup when done

Jiri Olsa
2020-05-12T12:12:41Z

On Tue, May 12, 2020 at 02:59:36PM +1000, Anand K Mistry wrote:

SNIP

> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 1ab349abe90469..099ecaa66732a2 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -53,6 +53,7 @@
> #include <unistd.h>
> #include <sched.h>
> #include <signal.h>
> +#include <sys/eventfd.h>
> #include <sys/mman.h>
> #include <sys/wait.h>
> #include <sys/types.h>
> @@ -518,15 +519,28 @@ static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size)
>
> static volatile int signr = -1;
> static volatile int child_finished;
> +static int done_fd = -1;
>
> static void sig_handler(int sig)
> {
> + u64 tmp = 1;
> if (sig == SIGCHLD)
> child_finished = 1;
> else
> signr = sig;
>
> done = 1;
> +
> + /*
> + * It is possible for this signal handler to run after done is checked
> + * in the main loop, but before the perf counter fds are polled. If this
> + * happens, the poll() will continue to wait even though done is set,
> + * and will only break out if either another signal is received, or the
> + * counters are ready for read. To ensure the poll() doesn't sleep when
> + * done is set, use an eventfd (done_fd) to wake up the poll().
> + */
> + if (write(done_fd, &tmp, sizeof(tmp)) < 0)
> + pr_err("failed to signal wakeup fd\n");
> }
>
> static void sigsegv_handler(int sig)
> @@ -1424,6 +1438,17 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
> int fd;
> float ratio = 0;
>
> + done_fd = eventfd(0, EFD_NONBLOCK);
> + if (done_fd < 0) {
> + pr_err("Failed to create wakeup eventfd, error: %m\n");
> + return -1;
> + }
> + err = evlist__add_pollfd(rec->evlist, done_fd);
> + if (err < 0) {
> + pr_err("Failed to add wakeup eventfd to poll list\n");
> + return -1;
> + }

sorry I did not notice before, but I think we also
need to close done_fd descriptor on the exit path

also please change subject to PATCHv3 for the next version

thanks,
jirka

> +
> atexit(record__sig_exit);
> signal(SIGCHLD, sig_handler);
> signal(SIGINT, sig_handler);
> --
> 2.26.2.645.ge9eca65c58-goog
>