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

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Date:   Thu, 1 Apr 2021 22:19:28 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Ioana Ciornei <ciorneiioana@...il.com>
Cc:     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 11:13:50PM +0300, Ioana Ciornei wrote:
> 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.

Nice. If you need to respin, consider putting this in patch 0/3.

      Andrew