On Mon, 2015-05-25 at 15:31 -0700, Eric Dumazet wrote: > On Mon, 2015-05-25 at 16:05 -0400, John A. Sullivan III wrote: > > Hello, all. One one of our connections we are doing intensive traffic > > shaping with tc. We are using ifb interfaces for shaping ingress > > traffic and we also use ifb interfaces for egress so that we can apply > > the same set of rules to multiple interfaces (e.g., tun and eth > > interfaces operating on the same physical interface). > > > > These are running on very powerful gateways; I have watched them > > handling 16 Gbps with CPU utilization at a handful of percent. Yet, I > > am seeing drops on the ifb interfaces when I do a tc -s qdisc show. > > > > Why would this be? I would expect if there was some kind of problem that > > it would manifest as drops on the physical interfaces and not the IFB > > interface. We have played with queue lengths in both directions. We > > are using HFSC with SFQ leaves so I would imagine this overrides the > > very short qlen on the IFB interfaces (32). These are drops and not > > overlimits. > > IFB is single threaded and a serious bottleneck. > > Don't use this on egress, this destroys multiqueue capaility. > > And SFQ is pretty limited (127 packets) > > You might try to change your NIC to have a single queue for RX, > so that you have a single cpu feeding your IFB queue. > > (ethtool -L eth0 rx 1) > > > > > Hmm . . . I've been thinking about that SFQ leaf qdisc. I see that newer kernels allow a much higher "limit" than 127 but it still seems that the queue depth limit for any one flow is still 127. When we do something like GRE/IPSec, I think the decrypted GRE traffic will distribute across the queues but the IPSec traffic will collapse all the packets initially into one queue. At 80ms RTT a 1 Gbps wire speed, I would need a queue of around 7500. Thus, can one say that SFQ is almost useless for high BDP connections?
Is there a similar round-robin type qdisc that does not have this limitation? If I recall correctly, if one does not attach a qdisc explicitly to a class, it defaults to pfifo_fast. Is that correct? Thanks - John -- 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
