I had posted the following on linux-net and haven't see any responses
possibly because nobody had any or that list is obsolete. I have been
told this is the current list for everything networking on linux so I
thought I'd try again...
I suspect the answer will be that it is what it is, but here's the
deal. I have a tool I use for monitoring network traffic among other
things - see http://collectl.sourceforge.net/ - and one of its benefits
is that you can run it continuously as a daemon (similar to sar) and
generate data in a format suitable for plotting. This means that you
can automate your entire network monitoring infrastructure at fairly
fine granularity, down to second if you like. Actually 1-second level
monitoring will provide incorrect data on earlier kernels because the
stats aren't updated on 1 second boundaries and you need to monitor at
an interval of 0.9765 seconds, but that's a different story which is
explained at http://collectl.sourceforge.net/NetworkStats.html
But more importantly, I've found that occasionally (not that often)
there is bogus data reported from /proc/net/dev. While I don't have a
lot of details on this it seems to only show up in 64 bit kernels. Look
at the following samples taken at 1 second intervals:
eth0:135115809 1024897 0 0 0 0 0 9
135458926 910340 0 0 0 0 0 0
eth0:135118023 1024923 0 0 0 0 0 9
135460952 910363 0 0 0 0 0 0
eth0: 0 884620 0 0 0 0 0 909397
9687563 1049736 0 0 0 0 0 0
eth0:135121189 1024957 0 0 0 0 0 9
135464222 910400 0 0 0 0 0 0
eth0:135129565 1024995 0 0 0 0 0 9
135473687 910435 0 0 0 0 0 0
see the middle sample? When I look at the change between samples it
generates a really big number since the difference is assumed to be
caused a counter wrapping. The problem is it's not always
straightforward when there is bad data. For example if the original and
bogus values are close enough it's not even clear there is a problem.
So the obvious question is, is there any way to prevent the bogus data
from getting reported? If not, is there any way to set the values to
something to indicate that the correct values can't be determined?
Clearly this problem would be visible to any tool that looks at /proc
but since many tools are not automated or don't take it to the level I
do, nobody probably notices. As for the counter update frequency, even
though they now appear to be updated closer to a 1 second boundary it
also means tools that can monitor at sub-second intervals will report
incorrect data since the counters only change once a second.
-mark
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