Add options to have fio latency profile a device
This adds three new options:
- latency_target. This defines a specific latency target, in usec.
- latency_window. This defines the period over which fio samples.
- latency_percentile. This defines the percentage of IOs that must
meet the criteria specified by latency_target/latency_window.
With these options set, fio will run the described workload and
vary the queue depth between 1 and iodepth= to find the best
performing spot that meets the criteria specified by the three
options.
A sample job file is also added to demonstrate how to use this.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/io_u.c b/io_u.c
index 7df57aa..ea6c251 100644
--- a/io_u.c
+++ b/io_u.c
@@ -1126,6 +1126,136 @@
return 0;
}
+static void lat_fatal(struct thread_data *td, struct io_completion_data *icd,
+ unsigned long tusec, unsigned long max_usec)
+{
+ if (!td->error)
+ log_err("fio: latency of %lu usec exceeds specified max (%lu usec)\n", tusec, max_usec);
+ td_verror(td, ETIMEDOUT, "max latency exceeded");
+ icd->error = ETIMEDOUT;
+}
+
+static void lat_new_cycle(struct thread_data *td)
+{
+ fio_gettime(&td->latency_ts, NULL);
+ td->latency_ios = ddir_rw_sum(td->io_blocks);
+ td->latency_failed = 0;
+}
+
+/*
+ * We had an IO outside the latency target. Reduce the queue depth. If we
+ * are at QD=1, then it's time to give up.
+ */
+static int __lat_target_failed(struct thread_data *td)
+{
+ if (td->latency_qd == 1)
+ return 1;
+
+ td->latency_qd_high = td->latency_qd;
+ td->latency_qd = (td->latency_qd + td->latency_qd_low) / 2;
+
+ dprint(FD_RATE, "Ramped down: %d %d %d\n", td->latency_qd_low, td->latency_qd, td->latency_qd_high);
+
+ /*
+ * When we ramp QD down, quiesce existing IO to prevent
+ * a storm of ramp downs due to pending higher depth.
+ */
+ io_u_quiesce(td);
+ lat_new_cycle(td);
+ return 0;
+}
+
+static int lat_target_failed(struct thread_data *td)
+{
+ if (td->o.latency_percentile.u.f == 100.0)
+ return __lat_target_failed(td);
+
+ td->latency_failed++;
+ return 0;
+}
+
+void lat_target_init(struct thread_data *td)
+{
+ if (td->o.latency_target) {
+ dprint(FD_RATE, "Latency target=%llu\n", td->o.latency_target);
+ fio_gettime(&td->latency_ts, NULL);
+ td->latency_qd = 1;
+ td->latency_qd_high = td->o.iodepth;
+ td->latency_qd_low = 1;
+ td->latency_ios = ddir_rw_sum(td->io_blocks);
+ } else
+ td->latency_qd = td->o.iodepth;
+}
+
+static void lat_target_success(struct thread_data *td)
+{
+ const unsigned int qd = td->latency_qd;
+
+ td->latency_qd_low = td->latency_qd;
+
+ /*
+ * If we haven't failed yet, we double up to a failing value instead
+ * of bisecting from highest possible queue depth. If we have set
+ * a limit other than td->o.iodepth, bisect between that.
+ */
+ if (td->latency_qd_high != td->o.iodepth)
+ td->latency_qd = (td->latency_qd + td->latency_qd_high) / 2;
+ else
+ td->latency_qd *= 2;
+
+ if (td->latency_qd > td->o.iodepth)
+ td->latency_qd = td->o.iodepth;
+
+ dprint(FD_RATE, "Ramped up: %d %d %d\n", td->latency_qd_low, td->latency_qd, td->latency_qd_high);
+ /*
+ * Same as last one, we are done
+ */
+ if (td->latency_qd == qd)
+ td->done = 1;
+
+ lat_new_cycle(td);
+}
+
+/*
+ * Check if we can bump the queue depth
+ */
+void lat_target_check(struct thread_data *td)
+{
+ uint64_t usec_window;
+ uint64_t ios;
+ double success_ios;
+
+ usec_window = utime_since_now(&td->latency_ts);
+ if (usec_window < td->o.latency_window)
+ return;
+
+ ios = ddir_rw_sum(td->io_blocks) - td->latency_ios;
+ success_ios = (double) (ios - td->latency_failed) / (double) ios;
+ success_ios *= 100.0;
+
+ dprint(FD_RATE, "Success rate: %.2f%% (target %.2f%%)\n", success_ios, td->o.latency_percentile.u.f);
+
+ if (success_ios >= td->o.latency_percentile.u.f)
+ lat_target_success(td);
+ else
+ __lat_target_failed(td);
+}
+
+/*
+ * If latency target is enabled, we might be ramping up or down and not
+ * using the full queue depth available.
+ */
+int queue_full(struct thread_data *td)
+{
+ const int qempty = io_u_qempty(&td->io_u_freelist);
+
+ if (qempty)
+ return 1;
+ if (!td->o.latency_target)
+ return 0;
+
+ return td->cur_depth >= td->latency_qd;
+}
struct io_u *__get_io_u(struct thread_data *td)
{
@@ -1136,7 +1266,7 @@
again:
if (!io_u_rempty(&td->io_u_requeues))
io_u = io_u_rpop(&td->io_u_requeues);
- else if (!io_u_qempty(&td->io_u_freelist)) {
+ else if (!queue_full(td)) {
io_u = io_u_qpop(&td->io_u_freelist);
io_u->buflen = 0;
@@ -1395,11 +1525,11 @@
icd->error = ops->io_u_lat(td, tusec);
}
- if (td->o.max_latency && tusec > td->o.max_latency) {
- if (!td->error)
- log_err("fio: latency of %lu usec exceeds specified max (%u usec)\n", tusec, td->o.max_latency);
- td_verror(td, ETIMEDOUT, "max latency exceeded");
- icd->error = ETIMEDOUT;
+ if (td->o.max_latency && tusec > td->o.max_latency)
+ lat_fatal(td, icd, tusec, td->o.max_latency);
+ if (td->o.latency_target && tusec > td->o.latency_target) {
+ if (lat_target_failed(td))
+ lat_fatal(td, icd, tusec, td->o.latency_target);
}
}