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

Arnaldo Carvalho de Melo
2020-05-12T14:12:28Z

Em Tue, May 12, 2020 at 02:12:32PM +0200, Jiri Olsa escreveu:
> 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

Yeah, and, and don't take this as a requirement for this patch to be
processed, this can be made as a follow up patch by you or someone else
(me, maybe :)), that maybe tools/perf/builtin-top.c and
tools/perf/builtin-trace.c have the same issue?

Could you please take a look there as well?

- Arnaldo

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

--

- Arnaldo