netdev - Re: ARM router NAT performance affected by random/unrelated commits

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Date:   Tue, 21 May 2019 11:45:12 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, John Crispin <john@...ozen.org>,
        Jonas Gorski <jonas.gorski@...il.com>,
        Jo-Philipp Wich <jo@...n.io>, Felix Fietkau <nbd@....name>
Subject: Re: ARM router NAT performance affected by random/unrelated commits

On Tue, May 21, 2019 at 12:28:48PM +0200, Rafał Miłecki wrote:
> Hi,
> 
> I work on home routers based on Broadcom's Northstar SoCs. Those devices
> have ARM Cortex-A9 and most of them are dual-core.
> 
> As for home routers, my main concern is network performance. That CPU
> isn't powerful enough to handle gigabit traffic so all kind of
> optimizations do matter. I noticed some unexpected changes in NAT
> performance when switching between kernels.
> 
> My hardware is BCM47094 SoC (dual core ARM) with integrated network
> controller and external BCM53012 switch.

Guessing, I'd say it's to do with the placement of code wrt cachelines.
You could try aligning some of the cache flushing code to a cache line
and see what effect that has.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up