On Tue, 2012-07-24 at 13:23 -0700, Jesse Brandeburg wrote:

> And to make e1000e more capable of processing packets you could
> consider turning on RPS to allow more cpus to process packets from the
> single interrupt that e1000e uses.
> 
...
> Yes, NAPI is actually making your system continue to run in the face of
> a DoS attack.  RPS will allow more CPUs to work on your receive
> traffic, which will allow more scaling.
> 
> see 
> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/main-network.html#s-network-future
> 
> for a nice description of RPS and how to enable it. suggest an rps_cpus
> value of 0xff to begin.  You may also want to consider enabling RFS
> while you're there, but start with RPS for simplicity.

Unfortunately, current linux network stack behaves not well if SYN
packets are distributed to all cpus, because they all contend on
listener socket lock.

RPS would be good, but to resist to SYN attacks its better to tweak it
so that all SYN packets are sent to a single CPU.

Its a single line change in net/core/flow_dissector.c

(or a hardware filter on ixgbe, not sure if it doable on igb ?)



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