On 3/6/07, Charles P Wright <[EMAIL PROTECTED]> wrote:
I have attached a patch to stat.cpp and stat.hpp that:
(1) Changes the type of M_counters to unsigned long long from unsigned
long
(2) Instead of tracking the count , average, and average of the squares in
M_counters and the sum and sum of squares separately in individual instance
variables just tracks the count, sum, and sum of squares in the M_counters
array.
(3) Creates a new function, computeMean that calculates the mean when
required (i.e., when it is displayed) rather than on every single update.
This has a few advantages:
(1) Because it uses unsigned long long exclusively there is no reason to
worry about lost precision anywhere.
(2) We only need to do the division for averages when it is needed, the
rest of the time we can just add.
Also, I couldn't locate where the periodic sums were reset; so either I
missed that spot in the original code or there was a bug.
Ok, will look to integrate this one too.
I also have a few questions/notes that I want to get some opinions on:
(1) The -trace_rtt option uses a different method of calculating the RTTs
than the RTD partitions and averages, would it make sense to unify the two
so that the observed and computed values are in sync?
Yes. It's a flaw.
(2) The update_nb option seems to take great care to avoid calling
getmilliseconds() on every loop. Is there a particular system that this
call is very expensive on?
That was our assumption. But if you prove us wrong, we could change this.
(3) The -trace_rtt option provides sub millisecond resolution, would it make
sense to provide that same resolution for the timing loop, and RTD counters?
If RTD counters are accurate to the ms, then this is already good. I don't
know if we need to go below this. Maybe you have a use case for this? The
-trace_rtt option was done with sub millisecond resolution, just for the
output format and compatibility with other tools we have.
Charles
--
Dr. Charles P. Wright
Research Staff Member
Network Server Systems Software
IBM T.J. Watson Research Center
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