netdev - Re: [PATCH net-next 3/8] cadence: macb: Add page pool support handle multi-descriptor frame rx

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Message-Id: <DFYQS9RIPCSY.25SHGGC3VM2M3@bootlin.com>
Date: Mon, 26 Jan 2026 19:45:29 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Andrew Lunn" <andrew@...n.ch>, "Paolo Valerio" <pvalerio@...hat.com>
Cc: <netdev@...r.kernel.org>, "Nicolas Ferre" <nicolas.ferre@...rochip.com>,
 "Claudiu Beznea" <claudiu.beznea@...on.dev>, "Andrew Lunn"
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>, "Lorenzo Bianconi" <lorenzo@...nel.org>,
 Théo Lebrun <theo.lebrun@...tlin.com>,
 Grégory Clement <gregory.clement@...tlin.com>, "Thomas
 Petazzoni" <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH net-next 3/8] cadence: macb: Add page pool support
 handle multi-descriptor frame rx

On Mon Jan 26, 2026 at 3:29 PM CET, Andrew Lunn wrote:
>> > I was more interested in plain networking, not XDP. Does it perform
>> > better with page pool? You at least need to show it is not worse, you
>> > need to avoid performance regressions.
>> 
>> I retested with iperf3. The target has a single rx queue with iperf3
>> running with no cpu affinity set.
>> 
>> |              |  64 | 128 |
>> | baseline     | 273 | 545 |
>> | pp (page)    | 273 | 544 |
>> | pp (2 frags) | 272 | 544 |
>
> So no real difference. That is unusual, it is typically faster, or if
> it is always doing line rate, it uses less CPU time. That might
> suggest the page pool integration is not optimal?

One more data point. I get line rate with & without page_pool so below
are CPU times from /proc/stat:

         upstream    pp
user            1     1
system        179    91 (!!!)
idle         7874  7303
softirq        35    37

16K pages on Mobileye EyeQ5 (MIPS), 7 fragments per page.

Paolo shared 64 versus 128 measurements but I am unsure what those stand
for; I doubt it can be packet size as xdp-bench does not have it as a
parameter. https://man.archlinux.org/man/extra/xdp-tools/xdp-bench.8.en

Measurement incantation:

   cat /proc/stat > /tmp/a && \
   iperf3 -c $IP && \
   cat /proc/stat > /tmp/b && \
   awk 'NR==FNR && $1=="cpu" {user=$2;sys=$4;idle=$5;softirq=$8;next}
        $1=="cpu" {printf "user\t%5d\n", $2-user}
        $1=="cpu" {printf "system\t%5d\n", $4-sys}
        $1=="cpu" {printf "idle\t%5d\n", $5-idle}
        $1=="cpu" {printf "softirq\t%5d\n", $8-softirq}
   ' /tmp/a /tmp/b

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com