On Wed, May 6, 2015 at 5:26 PM, Eric Dumazet <eduma...@google.com> wrote: > With the advent of small rto timers in datacenter TCP, > (ip route ... rto_min x), the following can happen : > > 1) Qdisc is full, transmit fails. > > TCP sets a timer based on icsk_rto to retry the transmit, without > exponential backoff. > With low icsk_rto, and lot of sockets, all cpus are servicing timer > interrupts like crazy. > Intent of the code was to retry with a timer between 200 (TCP_RTO_MIN) > and 500ms (TCP_RESOURCE_PROBE_INTERVAL) > > 2) Receivers can send zero windows if they don't drain their receive queue. > > TCP sends zero window probes, based on icsk_rto current value, with > exponential backoff. > With /proc/sys/net/ipv4/tcp_retries2 being 15 (or even smaller in > some cases), sender can abort in less than one or two minutes ! > If receiver stops the sender, it obviously doesn't care of very tight > rto. Probability of dropping the ACK reopening the window is not > worth the risk. > > Lets change the base timer to be at least 200ms (TCP_RTO_MIN) for these > events (but not normal RTO based retransmits) > > A followup patch adds a new SNMP counter, as it would have helped a lot > diagnosing this issue. > > Signed-off-by: Eric Dumazet <eduma...@google.com> > Signed-off-by: Yuchung Cheng <ych...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com> neal -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
