netdev - Re: Performance regression between 4.13 and 4.14

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Date:   Tue, 8 May 2018 10:10:27 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ben Greear <greearb@...delatech.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Performance regression between 4.13 and 4.14



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.