From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: [PATCH v2] net: Allow no-cache copy from user on transmit Date: Wed, 23 Mar 2011 11:51:23 -0700 Message-ID: <1300906283.25347.1467.camel@tardy> References: Reply-To: rick.jones2@hp.com Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org To: Tom Herbert Return-path: Received: from g1t0029.austin.hp.com ([15.216.28.36]:47809 "EHLO g1t0029.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755164Ab1CWSvZ (ORCPT ); Wed, 23 Mar 2011 14:51:25 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2011-03-23 at 10:10 -0700, Tom Herbert wrote: > This patch uses __copy_from_user_nocache (from skb_copy_to_page) > on transmit to bypass data cache for a performance improvement. > This functionality is configurable per device using ethtool, the > device must also be doing TX csum offload to enable. It seems > reasonable to set this when the netdevice does not copy or > otherwise touch the data. > > This patch was tested using 200 instances of netperf TCP_RR with > 1400 byte request and one byte reply. Platform is 16 core AMD x86. > > No-cache copy disabled: > 672703 tps, 97.13% utilization > 50/90/99% latency:244.31 484.205 1028.41 > > No-cache copy enabled: > 702113 tps, 96.16% utilization, > 50/90/99% latency 238.56 467.56 956.955 > > Using 14000 byte request and response sizes demonstrate the > effects more dramatically: > > No-cache copy disabled: > 79571 tps, 34.34 %utlization > 50/90/95% latency 1584.46 2319.59 5001.76 > > No-cache copy enabled: > 83856 tps, 34.81% utilization > 50/90/95% latency 2508.42 2622.62 2735.88 > > Note especially the effect on tail latency (95th percentile). > > This seems to provide a nice performance improvement and is > consistent in the tests I ran. Presumably, this would provide > the greatest benfits in the presence of an application workload > stressing the cache and a lot of transmit data happening. I don't > yet see a downside to using this. > > Signed-off-by: Tom Herbert Having raised the question about tying it to CKO and seeing it addressed to my satisfaction I'll go ahead and: Acked-by: Rick Jones rick jones