Re: TCP Performance advice needed [long!]

Ivan Voras wrote:

Ragnar Lonn wrote:
I don't know what tcp.inflight does but I know that this type of
application
protocol, that expects a reply before sending the next piece of data, will
always be completely dependent upon roundtrip times for its throughput -
the roundtrip time for the exchange "transmit-reply" will limit the
possible throughput you can get so if you want higher performance, either

I understand this bottleneck, and know (at least in theory :) ) how it
could be solved, but my problems are not directly related to that:

- For small (but consistent in size) packet sizes, I get randomly
varying round-trip times, and much lower packets-per-second ratio then
with big packets (consistent in size) with the exact same lock-step
protocol. Packet generation and processing are not CPU intensive.

This is because of the Nagle algo which tries to accumulate some more
data in packets and to piggyback ACKs to replies. Enable TCP_NODELAY
on the socket and it should go away. Disabling delayed ACKs may help
in your case too.

- When using big packets (actually, when switching back and forth from
small packets to big packets), the PPS performance starts low and climbs
to "normal" levels, and I'd like to avoid this. This is a local network
with 0 errors.

(if you like it, replace the word "packets" with "messages" in the above
explanation :) )

I think the above problems are not directly related to the protocol
(which could be better, I agree, but it won't happen at least until I
understand what is happening with this version) but on fine-tuning of
the network or socket options.

This is 'normal' TCP socket behaviour which is obviously not good with
your application.

--
Andre
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