Re: multicast performance

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On Thu, Nov 05, 2009 at 05:02:25PM +0100, Marco P. wrote:
> - Multicast performance decreases with the number of senders.
> I.e. if a single process can send data at 800Mbit/s, then two
> senders  (most likely) won't be able to send data at 400Mbit/s
> each.  (just saying that since you're using "many" servers)

That's good to know.  Can you be more specific?  Do you know what
kind of loss factor we can expect with each additional process?

Also, right now, we are more concerned with latency than throughput.
Our total traffic is less than what the hardware can handle from a
throughput perspective, but we are more senstive to latency issues.

> - Timestamping after receive() can be very imprecise.  You should
> probably use in-kernel timestamping for that purpose.

Also good to know.  I'm not familiar with kernel timestamping, but
will certainly look into it.

On the other hand, timestamping after the recv() call is still a
useful metric, since we can't use the data until we call recv().
However, more precise timestamping would allow us to further
pinpoint the exact location of the delay(s).

Thank you,

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