t/io_uring: don't track IO latencies the first second of runtime

The most variation is usually seen at startup, so don't start tracking
latencies until we've done the first reporting run. Things should be
nice and stable at that point.

To make this cheaper on the fast path, clock_index is only valid if
it's non-zero. This makes checking for stats cheap in the reap path.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/t/io_uring.c b/t/io_uring.c
index 5132927e47141ebfe39a28de811ebc09d5baa81e..2ae65bc19bb1dc487bbe176274743f6eb87e0fe6 100644 (file)
--- a/t/io_uring.c
+++ b/t/io_uring.c
@@ -102,6 +102,7 @@ struct submitter {
 
 static struct submitter *submitter;
 static volatile int finish;
+static int stats_running;
 
 static int depth = DEPTH;
 static int batch_submit = BATCH_SUBMIT;
@@ -442,7 +443,7 @@ static void init_io(struct submitter *s, unsigned index)
        sqe->ioprio = 0;
        sqe->off = offset;
        sqe->user_data = (unsigned long) f->fileno;
-       if (stats)
+       if (stats && stats_running)
                sqe->user_data |= ((unsigned long)s->clock_index << 32);
 }
 
@@ -527,8 +528,8 @@ static int reap_events_uring(struct submitter *s)
                                        stat_nr = 0;
                                }
                                last_idx = clock_index;
-                       }
-                       stat_nr++;
+                       } else if (clock_index)
+                               stat_nr++;
                }
                reaped++;
                head++;
@@ -559,7 +560,7 @@ static int submitter_init(struct submitter *s)
        if (stats) {
                nr_batch = roundup_pow2(depth / batch_submit);
                s->clock_batch = calloc(nr_batch, sizeof(unsigned long));
-               s->clock_index = 0;
+               s->clock_index = 1;
 
                s->plat = calloc(PLAT_NR, sizeof(unsigned long));
        } else {
@@ -602,7 +603,7 @@ static int prep_more_ios_aio(struct submitter *s, int max_ios, struct iocb *iocb
                                s->iovecs[index].iov_len, offset);
 
                data = f->fileno;
-               if (stats)
+               if (stats && stats_running)
                        data |= ((unsigned long) s->clock_index << 32);
                iocb->data = (void *) (uintptr_t) data;
                index++;
@@ -633,8 +634,8 @@ static int reap_events_aio(struct submitter *s, struct io_event *events, int evs
                                        stat_nr = 0;
                                }
                                last_idx = clock_index;
-                       }
-                       stat_nr++;
+                       } else if (clock_index)
+                               stat_nr++;
                }
                reaped++;
                evs--;
@@ -1281,6 +1282,11 @@ int main(int argc, char *argv[])
                /* don't print partial run, if interrupted by signal */
                if (finish)
                        break;
+
+               /* one second in to the run, enable stats */
+               if (stats)
+                       stats_running = 1;
+
                for (j = 0; j < nthreads; j++) {
                        this_done += s->done;
                        this_call += s->calls;