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Date: Sat, 8 Mar 2014 19:53:01 -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 Hi Eric, We noticed many changes in the TCP stack, and a lot of them come from you :-) Actually, we have a question about this patch you submitted (http://lwn.net/Articles/564979/) regarding an experiment we conducted in the 3.12.0 kernel. The results we observed in shown in the second figure of panel 6 in this poster at http://www.fsl.cs.sunysb.edu/~mchen/fast14poster-hashcast-portrait.pdf . We have repeated the same experiment for 100 times, and observed that results like that appeared 4 times. For this experiment, we observed that all five flows are using dedicated tx queues. But what makes a big difference is the average packet sizes of the flows. Client4 has an average packet size of around 3KB while all other clients generate packet sizes over 50KB. We suspect it might be caused by this TSO Packets Automatic Sizing feaure. Our reasoning is this: if a TCP flow starts slowly, this feature will assign it a small packet size. The packet size and the sending rate can somehow form a feedback loop, which can force the TCP flow's rate to stay low. What do you think about this? We have not tried the latest kernel yet. Frankly speaking, as a networking layman, I am already overwhelmed by the complexity of the TCP stack in the 3.12.0 kernel. I guess it is the nature of networking if we are going to 40GbE or even 100GbE. But anyway, thanks for your suggestion. Best, Ming On Sat, Mar 8, 2014 at 11:08 AM, Eric Dumazet <eric.dumazet@...il.com> wrote: > Also try more recent kernels. TCP stack changes a lot these days ;) > > http://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git > > contains many TCP related stuff which should land in linux-3.15 > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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