From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Performance regression between 4.13 and 4.14 Date: Wed, 9 May 2018 11:43:17 -0700 Message-ID: <17a364e0-89c8-d4f6-3873-353c7dae4fba@candelatech.com> References: <9115910b-dd8b-e7f3-be53-f739b8382032@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit To: Eric Dumazet , netdev Return-path: Received: from mail2.candelatech.com ([208.74.158.173]:36556 "EHLO mail2.candelatech.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933577AbeEISnT (ORCPT ); Wed, 9 May 2018 14:43:19 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 05/08/2018 10:10 AM, Eric Dumazet wrote: > > > On 05/08/2018 09:44 AM, Ben Greear wrote: >> Hello, >> >> I am trying to track down a performance regression that appears to be between 4.13 >> and 4.14. >> >> I first saw the problem with a hacked version of pktgen on some ixgbe NICs. 4.13 can do >> right at 10G bi-directional on two ports, and 4.14 and later can do only about 6Gbps. >> >> I also tried with user-space UDP traffic on a stock kernel, and I can get about 3.2Gbps combined tx+rx >> on 4.14 and about 4.4Gbps on 4.13. >> >> Attempting to bisect seems to be triggering a weirdness in git, and also lots of commits >> crash or do not bring up networking, which makes the bisect difficult. >> >> Looking at perf top, it would appear that some lock is probably to blame. > > > perf record -a -g -e cycles:pp sleep 5 > perf report > > Then you'll be able to tell us which lock (or call graph) is killing your perf. > I seem to be chasing multiple issues. For 4.13, at least part of my problem was that LOCKDEP was enabled, during my bisect, though it does NOT appear enabled in 4.16. I think maybe CONFIG_LOCKDEP moved to CONFIG_PROVE_LOCKING in 4.16, or something like that? My 4.16 .config does have CONFIG_LOCKDEP_SUPPORT enabled, and I see no option to disable it: [greearb@ben-dt3 linux-4.16.x64]$ grep LOCKDEP .config CONFIG_LOCKDEP_SUPPORT=y For 4.16, I am disabling RETRAMPOLINE...are there any other such things I need to disable to keep from getting a performance hit from the spectre-related bug fixes? At this point, I do not care about the security implications. greearb@ben-dt3 linux-4.16.x64]$ grep RETPO .config # CONFIG_RETPOLINE is not set Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com