netdev - Re: [PATCH net-next 2/3] dpaa2-eth: add rx copybreak support

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Message-ID: <20210401201350.vxyivlvvur6iqdp4@skbuf>
Date:   Thu, 1 Apr 2021 23:13:50 +0300
From:   Ioana Ciornei <ciorneiioana@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Ioana Ciornei <ciorneiioana@...il.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        ruxandra.radulescu@....com, Ioana Ciornei <ioana.ciornei@....com>
Subject: Re: [PATCH net-next 2/3] dpaa2-eth: add rx copybreak support

On Thu, Apr 01, 2021 at 08:49:43PM +0200, Andrew Lunn wrote:
> Hi Ioana
> 
> > +#define DPAA2_ETH_DEFAULT_COPYBREAK	512
> 
> This is quite big. A quick grep suggest other driver use 256.
> 
> Do you have some performance figures for this? 
> 

Hi Andrew,

Yes, I did some tests which made me end up with this default value.

A bit about the setup - a LS2088A SoC, 8 x Cortex A72 @ 1.8GHz, IPfwd
zero loss test @ 20Gbit/s throughput.  I tested multiple frame sizes to
get an idea where is the break even point.

Here are 2 sets of results, (1) is the baseline and (2) is just
allocating a new skb for all frames sizes received (as if the copybreak
was even to the MTU). All numbers are in Mpps.

         64   128    256   512  640   768   896

(1)     3.23  3.23  3.24  3.21  3.1  2.76  2.71
(2)     3.95  3.88  3.79  3.62  3.3  3.02  2.65

It seems that even for 512 bytes frame sizes it's comfortably better when
allocating a new skb. After that, we see diminishing rewards or even worse.

Ioana