perf bench: Fix div-by-zero if runtime is zero

Fix div-by-zero if runtime is zero:

  $ perf bench futex hash --runtime=0
  # Running 'futex/hash' benchmark:
  Run summary [PID 12090]: 4 threads, each operating on 1024 [private] futexes for 0 secs.
  Floating point exception (core dumped)
Signed-off-by: NTommi Rantala <tommi.t.rantala@nokia.com>
Acked-by: NJiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lore.kernel.org/lkml/20200417132330.119407-4-tommi.t.rantala@nokia.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bench/epoll-wait.c

@@ -519,7 +519,8 @@ int bench_epoll_wait(int argc, const char **argv)
 		qsort(worker, nthreads, sizeof(struct worker), cmpworker);
 
 	for (i = 0; i < nthreads; i++) {
-		unsigned long t = worker[i].ops / bench__runtime.tv_sec;
+		unsigned long t = bench__runtime.tv_sec > 0 ?
+			worker[i].ops / bench__runtime.tv_sec : 0;
 
 		update_stats(&throughput_stats, t);
 

tools/perf/bench/futex-hash.c

@@ -205,7 +205,8 @@ int bench_futex_hash(int argc, const char **argv)
 	pthread_mutex_destroy(&thread_lock);
 
 	for (i = 0; i < nthreads; i++) {
-		unsigned long t = worker[i].ops / bench__runtime.tv_sec;
+		unsigned long t = bench__runtime.tv_sec > 0 ?
+			worker[i].ops / bench__runtime.tv_sec : 0;
 		update_stats(&throughput_stats, t);
 		if (!silent) {
 			if (nfutexes == 1)

tools/perf/bench/futex-lock-pi.c

@@ -211,7 +211,8 @@ int bench_futex_lock_pi(int argc, const char **argv)
 	pthread_mutex_destroy(&thread_lock);
 
 	for (i = 0; i < nthreads; i++) {
-		unsigned long t = worker[i].ops / bench__runtime.tv_sec;
+		unsigned long t = bench__runtime.tv_sec > 0 ?
+			worker[i].ops / bench__runtime.tv_sec : 0;
 
 		update_stats(&throughput_stats, t);
 		if (!silent)