[ovs-dev] [PATCH] ofproto-dpif: Simplify subfacet stat calculations.

Ben Pfaff blp at nicira.com
Thu May 30 23:38:07 UTC 2013


On Thu, May 30, 2013 at 02:45:12PM -0700, Ethan Jackson wrote:
> Along with some minor minor cleanups, this patch simplifies the
> calculation of the average subfacet count, and average subfacet
> lifespan.  They are both calculated as exponentially weighted
> moving averages updated immediately after statistics are pulled
> from the datapath.  This both simplifies the code, and makes the
> statistics produced more useful.  Specifically, with the average
> total subfacet lifespan, subfacets which are still in the datapath
> now count towards that average.

I think (without really looking at it) that the previous code for
average subfacet lifespan calculated a genuine average over every
subfacet that ever existed.  The new version weights currently
existing subfacets the highest (but also gives them some additional
credit for all the time they existed previously--is that kosher?).
Subfacets that have expired receive exponentially decaying weight, so
that a subfacet that disappeared 10 seconds ago essentially disappears
from the average too.  That's a pretty different (and much
shorter-term) statistic.

If you want to include subfacets currently in the datapath, then you
could fold those in with a loop similar to the one that you added in
this patch.



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