From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raghavendra K T Subject: Re: [PATCH RFC 0/2] Optimize the snmp stat aggregation for large cpus Date: Tue, 25 Aug 2015 21:25:41 +0530 Message-ID: <55DC8FFD.2020306@linux.vnet.ibm.com> References: <1440489266-31127-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <1440513231.8932.14.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, kuznet@ms2.inr.ac.ru, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, jiri@resnulli.us, edumazet@google.com, hannes@stressinduktion.org, tom@herbertland.com, azhou@nicira.com, ebiederm@xmission.com, ipm@chirality.org.uk, nicolas.dichtel@6wind.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, anton@au1.ibm.com, nacc@linux.vnet.ibm.com, srikar@linux.vnet.ibm.com To: Eric Dumazet Return-path: In-Reply-To: <1440513231.8932.14.camel@edumazet-glaptop2.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 08/25/2015 08:03 PM, Eric Dumazet wrote: > On Tue, 2015-08-25 at 13:24 +0530, Raghavendra K T wrote: >> While creating 1000 containers, perf is showing lot of time spent in >> snmp_fold_field on a large cpu system. >> >> The current patch tries to improve by reordering the statistics gathering. >> >> Please note that similar overhead was also reported while creating >> veth pairs https://lkml.org/lkml/2013/3/19/556 >> >> Setup: >> 160 cpu (20 core) baremetal powerpc system with 1TB memory > > I wonder if these kind of results would demonstrate cache coloring > problems on this host. Looks like all the per cpu data are colliding on > same cache lines. > It could be. My testing on a 128 cpu system with less memory did not incur huge time penalty for 1000 containers. But snmp_fold_field in general had the problem. for e.g. same experiment I had around 15% overhead for snmp_fold reduced to 5% after the patch.