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.
background: fio's --client option could prove *extremely* useful for work where
we inject I/O workload from tens, hundreds or even thousands of VMs to an
OpenStack, container or other virtualization environment. I really like this
feature combined with "fio --server --daemonize=/var/run/fio-svr.pid" command
run on workload generators, because it means that we don't have to use ssh/pdsh
to start up a connection and launch the workload generator on each host. ssh
is problematic for this, I have to throttle it because it locks up if you have
too many concurrent ssh sessions starting up. pdsh is better but still has
limits because you actually have to start each thread up from scratch,
sometimes in competition with the workload you want to measure.
--- stat.c.sav 2015-01-23 16:22:14.566717417 -0500
+++ stat.c 2015-01-23 16:49:53.287962156 -0500
@@ -674,7 +674,8 @@
struct group_run_stats *rs, int ddir, struct json_object
*parent)
{
unsigned long min, max;
- unsigned long long bw, iops;
+ unsigned long long bw;
+ double iops;
unsigned int *ovals = NULL;
double mean, dev;
unsigned int len, minv, maxv;
@@ -698,12 +699,12 @@
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]);
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