stats: Add a function to report completion latency percentiles
This patch introduces two new options:
1) Specifying --clat_percentiles enables the reporting of
completion latency percentiles.
2) --percentile_list allows the user to customize the
list of percentiles to report.
Signed-off-by: Yu-ju Hong <yjhong@google.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/stat.c b/stat.c
index 8be4be5..25dd179 100644
--- a/stat.c
+++ b/stat.c
@@ -28,6 +28,134 @@
memcpy(&ts->ru_start, &ts->ru_end, sizeof(ts->ru_end));
}
+/*
+ * Given a latency, return the index of the corresponding bucket in
+ * the structure tracking percentiles.
+ *
+ * (1) find the group (and error bits) that the value (latency)
+ * belongs to by looking at its MSB. (2) find the bucket number in the
+ * group by looking at the index bits.
+ *
+ */
+static unsigned int plat_val_to_idx(unsigned int val)
+{
+ unsigned int msb, error_bits, base, offset, idx;
+
+ /* Find MSB starting from bit 0 */
+ if (val == 0)
+ msb = 0;
+ else
+ msb = (sizeof(val)*8) - __builtin_clz(val) - 1;
+
+ /* MSB <= (FIO_IO_U_PLAT_BITS-1), cannot be rounded off. Use
+ * all bits of the sample as index */
+ if (msb <= FIO_IO_U_PLAT_BITS)
+ return val;
+
+ /* Compute the number of error bits to discard*/
+ error_bits = msb - FIO_IO_U_PLAT_BITS;
+
+ /* Compute the number of buckets before the group */
+ base = (error_bits + 1) << FIO_IO_U_PLAT_BITS;
+
+ /* Discard the error bits and apply the mask to find the
+ * index for the buckets in the group */
+ offset = (FIO_IO_U_PLAT_VAL - 1) & (val >> error_bits);
+
+ /* Make sure the index does not exceed (array size - 1) */
+ idx = (base + offset) < (FIO_IO_U_PLAT_NR - 1)?
+ (base + offset) : (FIO_IO_U_PLAT_NR - 1);
+
+ return idx;
+}
+
+/*
+ * Convert the given index of the bucket array to the value
+ * represented by the bucket
+ */
+static unsigned int plat_idx_to_val(unsigned int idx)
+{
+ unsigned int error_bits, k, base;
+
+ assert(idx < FIO_IO_U_PLAT_NR);
+
+ /* MSB <= (FIO_IO_U_PLAT_BITS-1), cannot be rounded off. Use
+ * all bits of the sample as index */
+ if (idx < (FIO_IO_U_PLAT_VAL << 1) )
+ return idx;
+
+ /* Find the group and compute the minimum value of that group */
+ error_bits = (idx >> FIO_IO_U_PLAT_BITS) -1;
+ base = 1 << (error_bits + FIO_IO_U_PLAT_BITS);
+
+ /* Find its bucket number of the group */
+ k = idx % FIO_IO_U_PLAT_VAL;
+
+ /* Return the mean of the range of the bucket */
+ return base + ((k + 0.5) * (1 << error_bits));
+}
+
+static int double_cmp(const void *a, const void *b)
+{
+ const double fa = *(const double *)a;
+ const double fb = *(const double *)b;
+ int cmp = 0;
+
+ if (fa > fb)
+ cmp = 1;
+ else if (fa < fb)
+ cmp = -1;
+
+ return cmp;
+}
+
+/*
+ * Find and display the p-th percentile of clat
+ */
+static void show_clat_percentiles(unsigned int* io_u_plat, unsigned long nr,
+ double* user_list)
+{
+ unsigned long sum = 0;
+ unsigned int len, i, j = 0;
+ static const double def_list[FIO_IO_U_LIST_MAX_LEN] = {
+ 1.0, 5.0, 10.0, 20.0, 30.0,
+ 40.0, 50.0, 60.0, 70.0, 80.0,
+ 90.0, 95.0, 99.0, 99.5, 99.9};
+
+ const double* plist = user_list? user_list: def_list;
+ for (len = 0; len <FIO_IO_U_LIST_MAX_LEN && plist[len] != 0; len++) {}
+
+ /* Sort the user-specified list. Note that this does not work
+ for NaN values */
+ if (user_list && len > 1)
+ qsort((void*)user_list, len, sizeof(user_list[0]), double_cmp);
+
+ int is_last = 0;
+ log_info(" clat percentiles (usec) :");
+
+ for (i = 0; i <FIO_IO_U_PLAT_NR && !is_last; i++) {
+ sum += io_u_plat[i];
+ while (sum >= (plist[j]/100 * nr)) {
+ assert(plist[j] <= 100.0);
+
+ if (j!=0 && (j%4) == 0) /* for formatting */
+ log_info(" ");
+
+ /* end of the list */
+ is_last = (j == len - 1);
+
+ log_info(" %2.2fth=%u%c", plist[j], plat_idx_to_val(i),
+ (is_last? '\n' : ','));
+
+ if (is_last) break;
+
+ if (j%4 == 3) /* for formatting */
+ log_info("\n");
+ j++;
+ }
+ }
+}
+
static int calc_lat(struct io_stat *is, unsigned long *min, unsigned long *max,
double *mean, double *dev)
{
@@ -228,6 +356,11 @@
free(minp);
free(maxp);
}
+ if (ts->clat_percentiles) {
+ show_clat_percentiles(ts->io_u_plat[ddir],
+ ts->clat_stat[ddir].samples,
+ ts->percentile_list);
+ }
if (calc_lat(&ts->bw_stat[ddir], &min, &max, &mean, &dev)) {
double p_of_agg;
@@ -565,6 +698,12 @@
ts = &threadstats[j];
+ ts->clat_percentiles = td->o.clat_percentiles;
+ if (td->o.overwrite_plist)
+ ts->percentile_list = td->o.percentile_list;
+ else
+ ts->percentile_list = NULL;
+
idx++;
ts->members++;
@@ -636,6 +775,10 @@
for (k = 0; k <= 2; k++) {
ts->total_io_u[k] += td->ts.total_io_u[k];
ts->short_io_u[k] += td->ts.short_io_u[k];
+
+ int m;
+ for (m = 0; m < FIO_IO_U_PLAT_NR; m++)
+ ts->io_u_plat[k][m] += td->ts.io_u_plat[k][m];
}
ts->total_run_time += td->ts.total_run_time;
@@ -774,6 +917,15 @@
__add_log_sample(iolog, val, ddir, bs, mtime_since_genesis());
}
+static void add_clat_percentile_sample(struct thread_stat *ts,
+ unsigned long usec, enum fio_ddir ddir)
+{
+ unsigned int idx = plat_val_to_idx(usec);
+ assert(idx < FIO_IO_U_PLAT_NR);
+
+ ts->io_u_plat[ddir][idx]++;
+}
+
void add_clat_sample(struct thread_data *td, enum fio_ddir ddir,
unsigned long usec, unsigned int bs)
{
@@ -786,6 +938,9 @@
if (ts->clat_log)
add_log_sample(td, ts->clat_log, usec, ddir, bs);
+
+ if (ts->clat_percentiles)
+ add_clat_percentile_sample(ts, usec, ddir);
}
void add_slat_sample(struct thread_data *td, enum fio_ddir ddir,