Re: [Xen-devel] TSQ accounting skb->truesize degrades throughput for large packets

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

On Fri, 2013-09-06 at 10:00 -0700, Eric Dumazet wrote:
> On Fri, 2013-09-06 at 17:36 +0100, Zoltan Kiss wrote:
> 
> > So I guess it would be good to revisit the default value of this 
> > setting.
> 
> If ixgbe requires 3 TSO packets in TX ring to get line rate, you also
> can tweak dev->gso_max_size from 65535 to 64000.

Another idea would be to no longer use tcp_limit_output_bytes but

max(sk_pacing_rate / 1000, 2*MSS)

This means that number of packets in FQ would be limited to the
equivalent of 1ms, so TCP could have faster response to packet losses : 

Retransmitted packets would not have to wait for prior packets being
drained from FQ

For a 8Gbps flow, 1Gbyte/s, sk_pacing_rate would be 2Gbyte, this would
translate to ~2 Mbytes in Qdisc/TX ring.

sk_pacing_rate was introduced in linux-3.12, but could be backported
easily.




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