From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: Performance regression between 4.13 and 4.14 Date: Wed, 9 May 2018 11:48:50 -0700 Message-ID: <988a00db-bab3-7318-5e31-2a7c0948262a@gmail.com> References: <9115910b-dd8b-e7f3-be53-f739b8382032@candelatech.com> <17a364e0-89c8-d4f6-3873-353c7dae4fba@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: Ben Greear , Eric Dumazet , netdev Return-path: Received: from mail-pl0-f43.google.com ([209.85.160.43]:36006 "EHLO mail-pl0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935467AbeEISsw (ORCPT ); Wed, 9 May 2018 14:48:52 -0400 Received: by mail-pl0-f43.google.com with SMTP id v24-v6so4823047plo.3 for ; Wed, 09 May 2018 11:48:52 -0700 (PDT) In-Reply-To: <17a364e0-89c8-d4f6-3873-353c7dae4fba@candelatech.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 05/09/2018 11:43 AM, Ben Greear wrote: > 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 > No idea really, you mention a 4.13 -> 4.14 regression and jump then to 4.16 :/ Before doing a (painful) dissection, the perf output would immediately tell you if something is really wrong on your .config.