netdev - Performance regression between 4.13 and 4.14

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Message-ID: <9115910b-dd8b-e7f3-be53-f739b8382032@candelatech.com>
Date:   Tue, 8 May 2018 09:44:06 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     netdev <netdev@...r.kernel.org>
Subject: Performance regression between 4.13 and 4.14

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.

Any ideas what might have been introduced during this interval that
would cause this?

Anyone else seen similar?

I'm going to attempt some more manual steps to try to find the commit that
introduces this...

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com