Our MPI-based applications involve communicating processes where message
delivery times have to be on the order of 100-200 MICROseconds, not 200
milliseconds. Therefore, Nagle is turned off via the TCP_NODELAY socket
option, and switched fast ethernet is used. Data aggregation suitable
for a fast typist is an impediment to MPI, where delays must be 1000
times shorter.
Sincerely,
Josip
Rogier Wolff wrote:
>
> David Miller wrote:
> >
> > 2) Even if your fix was to be the final one, we have to be careful,
> > as just blindly ACK'ing immediately for small PSH packets is
> > deadly and will kill Nagle immediately. Actually the effect is
> > that nobody will be able to successfully perform Nagle to us.
>
>[...]
>
> I didn't look up RFC 896, but Richard steven says:
>
> We saw in 19.3 that the round trip time on an ethernet for a single
> byte to be sent, acknowledged, and echoed averaged around 16 ms. To
> generate data faster than this we would have to be typing more than 60
> characters per second. This means that we rarely encounter this
> algorithm when sending data between two hosts on a LAN.
>
> (TCP/IP illustrated, (first or second edition) page 267. section 19.4)
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