Re: [PATCH 1/2] RFC cyclictest: clean up --latency ordering in getopt

["Luis Claudio R. Goncalves" <lclaudio@uudg.org>]

On Mon, May 07, 2012 at 03:00:17PM -0700, Frank Rowand wrote:
| This is the resulting message on the ARM panda with a 'bad'
| 32khz timer:
| 
| 
|   # cyclictest -q -p 80 -t -n -l 10 -h ${hist_bins} -R 100
|   reported clock resolution: 1 nsec
|   measured clock resolution less than: 30517 nsec

How about using a fixed loop size (say 1000000 clock reads) to define
the average cost of reading the clock (the second value presented above)
instead of a variable amount of iterations? Reading the clock twice and
calculating the average could lead to wrong impressions. Also, it would
be interesting to run such test under a real time priority (FIFO:2, maybe?)
to avoid too much external interference on the readings, mainly involuntary
context switches.

Having too different values called 'clock resolution' may be a good source
of confusion. The value of clock_getres() is the resolution, as per the
system jargon, and the second value should be granularity, reading cost,
the-average-time-it-takes-to-read-the-clock or something alike.
 
| A possible follow on patch would be to generate a hard
| error (fail the test) if the measured resolution was
| above some unreasonable value (perhaps > 1 msec), but
| allow the hard fail to be overridden with yet another
| command line option.  Any opinions about that?

My suggestion is to keep the current behavior and add an option to
stop/complain case the clock has a poor resolution or has a reading
cost too high.

Luis
-- 
[ Luis Claudio R. Goncalves             Red Hat  -  Realtime Team ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]