Report latency for read, write and fsync separately in fileio tests

[mdcallag]

For sysbench fileio I want to see latency metrics for read, write and fsync. Today it reports one result, which I assume combines read and write and ignores fsync. But when one of the three is slow (read, write or fsync) then that is difficult to see with the current reporting.

The fio tool reports separate latency metrics for reads and writes, and after asking, Jens just added latency metrics for fsync. In my recent tests, fsync was by far the slowest operation and that slowness was confusing.

I know this is open source so I don't expect anyone to jump on this request, but it would be nice to have.

[akopytov]

Mark, yes, this is precisely what I'm working on right now: allow tests to define custom counters and latency histograms. fio reporting separate read/write stats was one of the examples I wanted to use to explain the feature.