netdev - Re: Optimizing kernel compilation / alignments for network performance

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Message-ID: <CAK8P3a1nR2VHYJsTy6aCz9qeZD0M2PYNyYgVwUj=_TOJvwCLwg@mail.gmail.com>
Date:   Fri, 6 May 2022 11:44:05 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Andrew Lunn <andrew@...n.ch>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Russell King <linux@...linux.org.uk>,
        Felix Fietkau <nbd@....name>,
        "openwrt-devel@...ts.openwrt.org" <openwrt-devel@...ts.openwrt.org>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: Optimizing kernel compilation / alignments for network performance

On Fri, May 6, 2022 at 10:55 AM Rafał Miłecki <zajec5@...il.com> wrote:
> On 6.05.2022 10:45, Arnd Bergmann wrote:
> > On Fri, May 6, 2022 at 9:44 AM Rafał Miłecki <zajec5@...il.com> wrote:
> >> With
> >> echo 1 > /sys/class/net/eth0/queues/rx-0/rps_cpus
> >> my NAT speeds were jumping between 2 speeds:
> >> 284 Mbps / 408 Mbps
> >
> > Can you try using 'numactl -C' to pin the iperf processes to
> > a particular CPU core? This may be related to the locality of
> > the user process relative to where the interrupts end up.
>
> I run iperf on x86 machines connected to router's WAN and LAN ports.
> It's meant to emulate end user just downloading from / uploading to
> Internet some data.
>
> Router's only task is doing masquarade NAT here.

Ah, makes sense. Can you observe the CPU usage to be on
a particular core in the slow vs fast case then?

        Arnd