Re: Timing overhead and Linux clock sources

On Mon, Aug 20, 2012 at 03:11:51PM -0400, Robert Haas wrote:
> On Thu, Aug 16, 2012 at 10:28 PM, Bruce Momjian <bruce@momjian.us> wrote:
> > FYI, I am planning to go ahead and package this tool in /contrib for PG
> > 9.3.
> 
> Isn't this exactly what we already did, in 9.2, in the form of
> contrib/pg_test_timing?

Sorry, not sure how I missed that commit.  Anyway, I am attaching a
patch for 9.3 that I think improves the output of the tool, plus adds
some C comments.

The new output has the lowest duration times first:

	Testing timing overhead for 3 seconds.
	Per loop time including overhead: 41.31 nsec
	Histogram of timing durations:
	< usec   % of total      count
	     1     95.87135   69627856
	     2      4.12759    2997719
	     4      0.00086        628
	     8      0.00018        133
	    16      0.00001          5
	    32      0.00000          1

This should make the output clearer to eyeball for problems --- a good
timing has a high percentage on the first line, rather than on the last
line.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +