Add gtod_cpu option for pinning gettimeofday() to a single CPU
Similar to what real life products sometimes do, offload gettimeofday()
calls to a single CPU and have that update the current time into a shared
memory location. This option pins a specific CPU for that job, and excludes
it from participating in any of the IO jobs.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index 5a87ae4..a58effc 100644
--- a/fio.c
+++ b/fio.c
@@ -55,6 +55,7 @@
static volatile int fio_abort;
static int exit_value;
static struct itimerval itimer;
+static pthread_t gtod_thread;
struct io_log *agg_io_log[2];
@@ -964,6 +965,18 @@
goto err;
}
+ if (td->o.gtod_cpu) {
+ if (fio_getaffinity(td->pid, &td->o.cpumask) == -1) {
+ td_verror(td, errno, "cpu_get_affinity");
+ goto err;
+ }
+ fio_cpu_clear(&td->o.cpumask, td->o.gtod_cpu);
+ if (fio_setaffinity(td) == -1) {
+ td_verror(td, errno, "cpu_set_affinity");
+ goto err;
+ }
+ }
+
if (td->ioprio_set) {
if (ioprio_set(IOPRIO_WHO_PROCESS, 0, td->ioprio) == -1) {
td_verror(td, errno, "ioprio_set");
@@ -1229,6 +1242,39 @@
terminate_threads(TERMINATE_ALL);
}
+static void *gtod_thread_main(void *data)
+{
+ fio_mutex_up(startup_mutex);
+
+ /*
+ * As long as we have jobs around, update the clock. It would be nice
+ * to have some way of NOT hammering that CPU with gettimeofday(),
+ * but I'm not sure what to use outside of a simple CPU nop to relax
+ * it - we don't want to lose precision.
+ */
+ while (threads) {
+ fio_gtod_update();
+ nop;
+ }
+
+ return NULL;
+}
+
+static int fio_start_gtod_thread(void)
+{
+ if (pthread_create(>od_thread, NULL, gtod_thread_main, NULL)) {
+ perror("Can't create gtod thread");
+ return 1;
+ }
+ if (pthread_detach(gtod_thread) < 0) {
+ perror("Can't detatch gtod thread");
+ return 1;
+ }
+
+ fio_mutex_down(startup_mutex);
+ return 0;
+}
+
/*
* Main function for kicking off and reaping jobs, as needed.
*/
@@ -1241,6 +1287,9 @@
if (fio_pin_memory())
return;
+ if (fio_gtod_offload && fio_start_gtod_thread())
+ return;
+
if (!terse_output) {
printf("Starting ");
if (nr_thread)