[PATCH] IO completion time histograms
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index e5b09fd..f61b4c1 100644
--- a/HOWTO
+++ b/HOWTO
@@ -556,6 +556,8 @@
bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
cpu : usr=1.49%, sys=0.25%, ctx=7969
IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
+ lat (msec): 2=1.6%, 4=0.0%, 8=3.2%, 16=12.8%, 32=38.4%, 64=24.8%, 128=15.2%
+ lat (msec): 256=4.0%, 512=0.0%, 1024=0.0%, >=2048=0.0%
The client number is printed, along with the group id and error of that
thread. Below is the io statistics, here for writes. In the order listed,
@@ -585,6 +587,12 @@
16= entries includes depths up to that value but higher
than the previous entry. In other words, it covers the
range from 16 to 31.
+IO latencies= The distribution of IO completion latencies. This is the
+ time from when IO leaves fio and when it gets completed.
+ The numbers follow the same pattern as the IO depths,
+ meaning that 2=1.6% means that 1.6% of the IO completed
+ within 2 msecs, 16=12.8% means that 12.8% of the IO
+ took more than 8 msecs, but less than (or equal to) 16 msecs.
After each client has been listed, the group statistics are printed. They
will look like this: