Re: fix TCP roundtrip time update code

[Nivedita Singhvi <niv@us.ibm.com>]

David Mosberger wrote:

>  $ httperf --rate 1000 --num-conns 1000000 --verbose --hog --server HOST \
> 	--uri pathto30KBfile

Hmm, ditto, except I was way down at --rate 300 (was seeing client
errors of fd-unavail). Have ulimited upwards but am still seeing
them..

> on 3 clients (for a total of 3000 conns/sec).  You can't go higher
> than 1000 conn/sec per client (IP address) because otherwise you run
> out of port space (due to TIME_WAIT).

You can hike /proc/sys/net/ipv4/tcp_tw_recycle for that.

> This load worked well for a machine with a single GigE card.  All
> network tunables were on the default setting (in particular, the tx
> queue len was 300, which is were the losses came from).
> 
> With this load, I saw bad RTT values in the route cache within a
> couple of seconds after starting the third httperf generator.  It then
> took a bit longer (on the order of 1-2 minutes) until the first
> TCPAbortFailed errors started to pop up

I saw a few AbortOnTimeouts, but no AbortFailed counts.

Those should be TCPAbortOnTimeout counts, rather than TCPAbortFailed
errors, I would expect? Why AbortFailed?  Coming from IP via
tcp_transmit_skb()?

thanks,
Nivedita