netdev - Re: [PATCH v3 net-next 7/8] net: mvneta: make tx buffer array agnostic

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Date:   Wed, 16 Oct 2019 11:18:43 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net,
        thomas.petazzoni@...tlin.com, brouer@...hat.com,
        matteo.croce@...hat.com, mw@...ihalf.com
Subject: Re: [PATCH v3 net-next 7/8] net: mvneta: make tx buffer array
 agnostic

Hi Jakub,

On Tue, Oct 15, 2019 at 05:03:53PM -0700, Jakub Kicinski wrote:
> On Mon, 14 Oct 2019 12:49:54 +0200, Lorenzo Bianconi wrote:
> > Allow tx buffer array to contain both skb and xdp buffers in order to
> > enable xdp frame recycling adding XDP_TX verdict support
> > 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >  drivers/net/ethernet/marvell/mvneta.c | 66 +++++++++++++++++----------
> >  1 file changed, 43 insertions(+), 23 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > index a79d81c9be7a..477ae6592fa3 100644
> > --- a/drivers/net/ethernet/marvell/mvneta.c
> > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > @@ -561,6 +561,20 @@ struct mvneta_rx_desc {
> >  };
> >  #endif
> >  
> > +enum mvneta_tx_buf_type {
> > +	MVNETA_TYPE_SKB,
> > +	MVNETA_TYPE_XDP_TX,
> > +	MVNETA_TYPE_XDP_NDO,
> > +};
> > +
> > +struct mvneta_tx_buf {
> > +	enum mvneta_tx_buf_type type;
> 
> I'd be tempted to try to encode type on the low bits of the pointer,
> otherwise you're increasing the cache pressure here. I'm not 100% sure
> it's worth the hassle, perhaps could be a future optimization.
> 

Since this is already offering a performance boost (since buffers are not
unmapped, but recycled and synced), we'll consider adding the buffer tracking
capability to the page_pool API. I don't think you'll see any performance
benefits on this device specifically (or any 1gbit interface), but your idea is
nice, if we add it on the page_pool API we'll try implementing it like that.

> > +	union {
> > +		struct xdp_frame *xdpf;
> > +		struct sk_buff *skb;
> > +	};
> > +};
> 


Thanks
/Ilias