From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Baron Subject: Re: [PATCH net-next v2] tcp: reduce cpu usage under tcp memory pressure when SO_SNDBUF is set Date: Tue, 11 Aug 2015 11:03:30 -0400 Message-ID: <55CA0EC2.9030306@akamai.com> References: <20150811143846.672A92039@prod-mail-relay10.akamai.com> <1439304576.1084.24.camel@edumazet-glaptop2.roam.corp.google.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: Eric Dumazet Return-path: Received: from a23-79-238-175.deploy.static.akamaitechnologies.com ([23.79.238.175]:16884 "EHLO prod-mail-xrelay07.akamai.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752281AbbHKPDb (ORCPT ); Tue, 11 Aug 2015 11:03:31 -0400 In-Reply-To: <1439304576.1084.24.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: On 08/11/2015 10:49 AM, Eric Dumazet wrote: > On Tue, 2015-08-11 at 14:38 +0000, Jason Baron wrote: >> From: Jason Baron > >> In my testing, this brought a single threaad's cpu usage down from 100% to ~1% >> while maintaining the same level of throughput. >> > > Hi Jason. Could you give more details on this test ? > > How many flows are competing ? > > Yes, so the test case I'm using to test against is somewhat contrived. In that I am simply allocating around 40,000 sockets that are idle to create a 'permanent' memory pressure in the background. Then, I have just 1 flow that sets SO_SNDBUF, which results in the: poll(), write() loop. That said, we encountered this issue initially where we had 10,000+ flows and whenever the system would get into memory pressure, we would see all the cpus spin at 100%. So the testcase I wrote, was just a simplistic version for testing. But I am going to try and test against the more realistic workload where this issue was initially observed. Thanks, -Jason