[ovs-dev] [PATCH] Initial implementation of sFlow.

[Justin Pettit]

On Jan 7, 2010, at 4:08 PM, Neil McKee wrote:

>> +	u64 sflow_pool;		/* Packets that could have been sampled. */
>> 
>> 
>> I think the sFlow definition for this is only 32-bit.  I'm guessing this is only increasing, since it's never reset any place.  I'm a bit surprised that the counters in sFlow are 32 bit in that case...
> 
> The sample-pool is send with every packet-sample,  so it only needs to have enough bits to avoid wrapping between samples.  You would only need more than 32-bits if you wanted a sampling rate of the order of 10^9,  and typical settings are more like 1-in-400.   The collector will take care of accumulating deltas from sample to sample,  using unsigned arithmetic to handle rollovers when they happen.

I thought that might be the case, but then I would have expected sflow_pool to be reset for each sample taken.  Right now, it only seems to be monotonically increasing.

--Justin