netdev - Re: [RFC PATCH v2] tcp: TCP Small Queues

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Date:	Thu, 12 Jul 2012 01:49:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>, ycheng@...gle.com,
	dave.taht@...il.com, netdev@...r.kernel.org,
	codel@...ts.bufferbloat.net, therbert@...gle.com,
	mattmathis@...gle.com, nanditad@...gle.com, ncardwell@...gle.com,
	andrewmcgr@...il.com
Subject: Re: [RFC PATCH v2] tcp: TCP Small Queues

On Wed, 2012-07-11 at 11:44 -0700, Rick Jones wrote:
> On 07/11/2012 08:11 AM, Eric Dumazet wrote:
> >
> > Some bench results about the choice of 128KB being the default value:
> 
> What were the starting/baseline figures?
> 
> >
> > Tests using a single TCP flow.
> >
> > Tests on 10Gbit links :
> >
> >
> > echo 16384 >/proc/sys/net/ipv4/tcp_limit_output_bytes
> > OMNI Send TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.99.2 (192.168.99.2) port 0 AF_INET
> > tcpi_rto 201000 tcpi_ato 0 tcpi_pmtu 1500 tcpi_rcv_ssthresh 14600
> > tcpi_rtt 1875 tcpi_rttvar 750 tcpi_snd_ssthresh 16 tpci_snd_cwnd 79
> > tcpi_reordering 53 tcpi_total_retrans 0
> > Local       Local       Local  Elapsed Throughput Throughput  Local Local  Remote Remote Local   Remote  Service
> > Send Socket Send Socket Send   Time               Units       CPU   CPU    CPU    CPU    Service Service Demand
> > Size        Size        Size   (sec)                          Util  Util   Util   Util   Demand  Demand  Units
> > Final       Final                                             %     Method %      Method
> > 392360      392360      16384  20.00   1389.53    10^6bits/s  0.52  S      4.30   S      0.737   1.014   usec/KB
> 
> By the way, that double reporting of the local socket send size is fixed in:
> 
> ------------------------------------------------------------------------
> r516 | raj | 2012-01-05 15:48:52 -0800 (Thu, 05 Jan 2012) | 1 line
> 
> report the rsr_size_end in an omni stream test rather than a copy of the 
> lss_size_end
> 
> of netperf and later.  Also, any idea why the local socket send size got 
> so much larger with 1GbE than 10 GbE at that setting of 
> tcp_limit_output_bytes?

The 10Gb receiver is a net-next kernel, but the 1Gb receiver is a 2.6.38
ubuntu kernel. They probably have very different TCP behavior.



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