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Re: [nm-wg] standard timestamp format
Dan Gunter wrote:
2. Single-source timestamps
(a) 64-bit counter (?)
Then you are suggesting that a #2 timestamp could be optionally
included wherever we allow a #1 timestamp.
Yes, and the units should be nanoseconds in a 64bit counter with
arbitrary zero point. The value is
quantized to whatever resolution the provider supports, e.g.
milliseconds for java, 10ms ticks for
Linux, about 1us for Solaris.
I would suggest that the units be an optional parameter, since they
aren't always needed, and maybe aren't always known, i.e. in the case of
some kind of hardware clock.
If you don't know the clock frequency then the data is meaningless,
the units should be nanoseconds and you should multiply whatever the
source clock rate is by some implementation and source specific factor
to get to nanoseconds. For the simplest portable java code that would
be 1000000 to go from milliseconds. Linux doesn't require a hires
counter but I think some implementations may have one, Solaris always
has gethrtime regardless of whether its on SPARC or x86, I know HP-UX,
AIX and windows have hires counters.
Adrian
There also needs to be a definition of the parameters that combined
together make up the signature of
the source. e.g. the pair of IP:port endpoints identifies a unique
flow for TCP/IP, whatever makes sense
for the network measurements in this case should be clear.
Good point. The source is what we are calling a "node", so I would say
that we should include the single-source timestamp node(s) in the
metadata along with the path endpoints and tool versions, etc. This same
metadata is where I would put the (optional) units.
Sound good to everyone else? I can pretty easily modify the current
report schema to do the above things. Maybe we should talk about it on
the next conference call (hint, hint).
-Dan
--
adrian.cockcroft@sun.com - Sun Microsystems Inc, Menlo Park, CA
Chief Architect - High Performance Technical Computing
Distinguished Engineer and Sun Sigma Black Belt
Phone/Fax: (650)352-5830, x49068
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