netdev - RE: [PATCH v2 net-next 0/8] dpaa2-eth: Introduce XDP support

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Message-ID: <AM0PR04MB4994069A30049AE6C34D442194AA0@AM0PR04MB4994.eurprd04.prod.outlook.com>
Date:   Fri, 7 Dec 2018 18:07:49 +0000
From:   Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
CC:     Jesper Dangaard Brouer <brouer@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Ioana Ciornei <ioana.ciornei@....com>,
        "dsahern@...il.com" <dsahern@...il.com>,
        Camelia Alexandra Groza <camelia.groza@....com>
Subject: RE: [PATCH v2 net-next 0/8] dpaa2-eth: Introduce XDP support

> -----Original Message-----
> From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Sent: Friday, December 7, 2018 7:52 PM
> To: Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>
> Cc: Jesper Dangaard Brouer <brouer@...hat.com>;
> netdev@...r.kernel.org; davem@...emloft.net; Ioana Ciornei
> <ioana.ciornei@....com>; dsahern@...il.com; Camelia Alexandra Groza
> <camelia.groza@....com>
> Subject: Re: [PATCH v2 net-next 0/8] dpaa2-eth: Introduce XDP support
> 
> Hi Ioana,
> > > > >
> > > I only did a quick grep around the driver so i might be missing something,
> > > but i can only see allocations via napi_alloc_frag(). XDP requires pages
> > > (either a single page per packet or a driver that does the page
> management
> > > of
> > > its own and fits 2 frames in a single page, assuming 4kb pages).
> > > Am i missing something on the driver?
> >
> > No, I guess I'm the one missing stuff, I didn't realise single page per packet
> > is a hard requirement for XDP. Could you point me to more info on this?
> >
> 
> Well if you don't have to use 64kb pages you can use the page_pool API (only
> used from mlx5 atm) and get the xdp recycling for free. The memory 'waste'
> for
> 4kb pages isn't too much if the platforms the driver sits on have decent
> amounts
> of memory  (and the number of descriptors used is not too high).
> We still have work in progress with Jesper (just posted an RFC)with
> improvements
> on the API.
> Using it is fairly straightforward. This is a patchset on marvell's mvneta
> driver with the API changes needed:
> https://www.spinics.net/lists/netdev/msg538285.html
> 
> If you need 64kb pages you would have to introduce page recycling and
> sharing
> like intel/mlx drivers on your driver.

Thanks a lot for the info, will look into this. Do you have any pointers
as to why the full page restriction exists in the first place? Sorry if it's
a dumb question, but I haven't found details on this and I'd really like
to understand it.

Thanks
Ioana