stat: use long doubles to identify latency percentiles

In some cases, the 100th percentile latency is not correctly identified
because of problems with double precision floating point arithmetic.
Use long doubles instead in the while loop condition to reduce the
likelihood of encountering this problem.

Also, print an error message when latency percentiles are not
successfully identified.

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

diff --git a/stat.c b/stat.c
index c1f46e1d43f34fe9a8988279780c269162d9084d..66a13bcad4347269f7532669027d3644c72ef040 100644 (file)
--- a/stat.c
+++ b/stat.c
@@ -170,7 +170,7 @@ unsigned int calc_clat_percentiles(uint64_t *io_u_plat, unsigned long long nr,
        is_last = false;
        for (i = 0; i < FIO_IO_U_PLAT_NR && !is_last; i++) {
                sum += io_u_plat[i];
-               while (sum >= (plist[j].u.f / 100.0 * nr)) {
+               while (sum >= ((long double) plist[j].u.f / 100.0 * nr)) {
                        assert(plist[j].u.f <= 100.0);
 
                        ovals[j] = plat_idx_to_val(i);
@@ -187,6 +187,9 @@ unsigned int calc_clat_percentiles(uint64_t *io_u_plat, unsigned long long nr,
                }
        }
 
+       if (!is_last)
+               log_err("fio: error calculating latency percentiles\n");
+
        *output = ovals;
        return len;
 }