From 9f68fe3abd9f2f9e31c681fc22d0e94b1c80cfff Mon Sep 17 00:00:00 2001 From: Ben England Date: Fri, 27 Feb 2015 08:14:49 -0700 Subject: [PATCH] Patch to make per-thread IOPS more accurate The following small patch to stat.c (using fio 2.2.4 from github) outputs IOPS field in JSON format as a floating point number instead of an integer. This improves accuracy in case where fio --client runs use lots of threads with single-digit IOPS per thread. It seems to work, here's a snippet of output from a short fio run with rate_iops=10 in the job file. "write" : { "io_bytes" : 6464, "bw" : 646, "iops" : 10.10, "runtime" : 10000, Why the patch: IOPS number is rounded to integer in stats.c calls to num2str(). This doesn't sound like much of a problem because in many use cases, with large IOPS number the error is negligible. But in this use case where we have many threads (we would like to get into the thousands eventually), the IOPS/thread may be quite low and integer rounding can introduce significant error. For example, if we are doing 5,000 IOPS over 1,000 threads, average throughput is 5 IOPS and potential error is ~20%, but some threads could have much higher error in IOPS because of integer format. Signed-off-by: Jens Axboe --- stat.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/stat.c b/stat.c index db4a3872..85bd728d 100644 --- a/stat.c +++ b/stat.c @@ -674,9 +674,9 @@ static void add_ddir_status_json(struct thread_stat *ts, struct group_run_stats *rs, int ddir, struct json_object *parent) { unsigned long min, max; - unsigned long long bw, iops; + unsigned long long bw; unsigned int *ovals = NULL; - double mean, dev; + double mean, dev, iops; unsigned int len, minv, maxv; int i; const char *ddirname[] = {"read", "write", "trim"}; @@ -693,17 +693,18 @@ static void add_ddir_status_json(struct thread_stat *ts, json_object_add_value_object(parent, ts->unified_rw_rep ? "mixed" : ddirname[ddir], dir_object); - iops = bw = 0; + bw = 0; + iops = 0.0; if (ts->runtime[ddir]) { uint64_t runt = ts->runtime[ddir]; bw = ((1000 * ts->io_bytes[ddir]) / runt) / 1024; - iops = (1000 * (uint64_t) ts->total_io_u[ddir]) / runt; + iops = (1000.0 * (uint64_t) ts->total_io_u[ddir]) / runt; } json_object_add_value_int(dir_object, "io_bytes", ts->io_bytes[ddir] >> 10); json_object_add_value_int(dir_object, "bw", bw); - json_object_add_value_int(dir_object, "iops", iops); + json_object_add_value_float(dir_object, "iops", iops); json_object_add_value_int(dir_object, "runtime", ts->runtime[ddir]); json_object_add_value_int(dir_object, "total_ios", ts->total_io_u[ddir]); json_object_add_value_int(dir_object, "short_ios", ts->short_io_u[ddir]); -- 2.25.1