netdev - Re: Serious performance degradation in Linux 4.15

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Message-ID: <20180216164853.GG25201@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Feb 2018 17:48:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Jon Maloy <jon.maloy@...csson.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "David Miller (davem@...emloft.net)" <davem@...emloft.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: Serious performance degradation in Linux 4.15

On Fri, Feb 16, 2018 at 02:38:39PM +0000, Matt Fleming wrote:
> On Wed, 14 Feb, at 10:46:20PM, Matt Fleming wrote:

> > Here's some more numbers. This is with RETPOLINE=y but you'll see it
> > doesn't make much of a difference. Oh, this is also with powersave
> > cpufreq governor.
> 
> Feh, I was wrong. The differences in performance I see are entirely
> due to CONFIG_RETPOLINE and CONFIG_PAGE_TABLE_ISOLATION being enabled.

OK, so I'm not the one crazy person not being able to reproduce this :-)

Lets wait for more details from the original submitter.