Re: Very high bandwith packet based interface and performance problems

[Rick Jones <raj@cup.hp.com>]

> > > This is NOT what I'm seeing at all.. the kernel load appears to be
> > > pegged at 100% (or very close to it), the user space app is getting
> > > enough cpu time to read out about 10-20Mbit, and FURTHERMORE the kernel
> > > appears to be ACKING ALL the traffic, which I don't understand at all
> > > (e.g. the transmitter is simply blasting 300MBit of tcp unrestricted)
> >
> > TCP _requires_ the remote end ack every 2nd frame regardless of progress.
> 
> YIPES. I didn't realize this was the case.. how is end-to-end application
> flow control handled when the bottle neck is user space bound and not b/w
> bound? e.g. if i write a test app that does a

If the app is not reading from the socket buffer, the receiving TCP is
supposed to stop sending window-updates, and the sender is supposed to
stop sending data when it runs-out of window.

If TCP ACK's data, it really should (must?) not then later drop it on
the floor without aborting the connection. If a TCP is ACKing data and
then that data is dropped before it is given to the application, and the
connection is not being reset, that is probably a bug.

A TCP _is_ free to drop data prior to sending an ACK - it simply drops
it and does not ACK it.

rick jones

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