netdev - Re: [BUG?] ixgbe: only num_online_cpus() of the tx queues are enabled

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Date:	Sun, 9 Mar 2014 01:47:27 -0500
From:	Ming Chen <v.mingchen@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, Erez Zadok <ezk@....cs.sunysb.edu>,
	Dean Hildebrand <dhildeb@...ibm.com>,
	Geoff Kuenning <geoff@...hmc.edu>
Subject: Re: [BUG?] ixgbe: only num_online_cpus() of the tx queues are enabled

On Sat, Mar 8, 2014 at 10:37 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> The feedback loop you mention should be solved by the patch I sent
> today : TCP Small queue make sure that you have no more than 2 packets
> per flow on qdisc / TX queues. So on 'fast' flow cannot have 90% of the
> packets in the qdisc. cwnd is maintained to very small values, assuming
> receiver is behaving normally.
>

Thanks for the patch. I forgot to mention that excessively big cwnd
(or bufferbloat) does play a part in Hash-Cast. We found that using
TCP Vegas does not show unfairness even in the presence of hash
collision among TCP flows. Comparing Vegas and Cubic, we found that
Vegas has a much smaller cwnd.

Best,
Ming
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