netdev - Re: [PATCH v2 3/6] net: ocelot: pre-compute injection frame header content

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Date:   Mon, 15 Nov 2021 11:58:05 +0100
From:   Clément Léger <clement.leger@...tlin.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 3/6] net: ocelot: pre-compute injection frame header
 content

Le Mon, 15 Nov 2021 10:51:45 +0000,
Vladimir Oltean <vladimir.oltean@....com> a écrit :

> > I checked again my bandwith numbers (obtained with iperf3) with and
> > without the pre-computed header:
> > 
> > Test on standard packets with UDP (iperf3 -t 100 -l 1460 -u -b 0 -c *)
> > - With pre-computed header: UDP TX: 	33Mbit/s
> > - Without UDP TX: 			31Mbit/s  
> > -> 6.5% improvement  
> > 
> > Test on small packets with UDP (iperf3 -t 100 -l 700 -u -b 0 -c *)
> > - With pre-computed header: UDP TX: 	15.8Mbit/s
> > - Without UDP TX: 			16.4Mbit/s  
> > -> 4.3% improvement  
> > 
> > The improvement might not be huge but also not negligible at all.
> > Please tell me if you want me to drop it or not based on those numbers.  
> 
> Is this with manual injection or with FDMA? Do you have before/after
> numbers with FDMA as well? At 31 vs 33 Mbps, this isn't going to compete
> for any races anyway :)

These numbers were for the FDMA, with the CPU, its even much lower
because more time is spent to push bytes through registers...
But agreed with that, this isn't going to beat any records !


-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com