Re: [PATCH v6 net-next 5/5] net: ethernet: ti: cpsw: add XDP support

[Ivan Khoronzhuk]

On Thu, Jul 04, 2019 at 11:19:39AM +0200, Jesper Dangaard Brouer wrote:
> On Wed,  3 Jul 2019 13:19:03 +0300
> Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:
>
> > Add XDP support based on rx page_pool allocator, one frame per page.
> > Page pool allocator is used with assumption that only one rx_handler
> > is running simultaneously. DMA map/unmap is reused from page pool
> > despite there is no need to map whole page.
> >
> > Due to specific of cpsw, the same TX/RX handler can be used by 2
> > network devices, so special fields in buffer are added to identify
> > an interface the frame is destined to. Thus XDP works for both
> > interfaces, that allows to test xdp redirect between two interfaces
> > easily. Aslo, each rx queue have own page pools, but common for both
> > netdevs.
> >
> > XDP prog is common for all channels till appropriate changes are added
> > in XDP infrastructure. Also, once page_pool recycling becomes part of
> > skb netstack some simplifications can be added, like removing
> > page_pool_release_page() before skb receive.
> >
> > In order to keep rx_dev while redirect, that can be somehow used in
> > future, do flush in rx_handler, that allows to keep rx dev the same
> > while reidrect. It allows to conform with tracing rx_dev pointed
> > by Jesper.
>
> So, you simply call xdp_do_flush_map() after each xdp_do_redirect().
> It will kill RX-bulk and performance, but I guess it will work.
>
> I guess, we can optimized it later, by e.g. in function calling
> cpsw_run_xdp() have a variable that detect if net_device changed
> (priv->ndev) and then call xdp_do_flush_map() when needed.

It's problem of cpsw already and can be optimized locally by own
bulk queues for instance, if it will be simple if really needed ofc.

> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
> > ---
> >  drivers/net/ethernet/ti/Kconfig        |   1 +
> >  drivers/net/ethernet/ti/cpsw.c         | 485 ++++++++++++++++++++++---
> >  drivers/net/ethernet/ti/cpsw_ethtool.c |  66 +++-
> >  drivers/net/ethernet/ti/cpsw_priv.h    |   7 +
> >  4 files changed, 502 insertions(+), 57 deletions(-)
> [...]
> > +static int cpsw_run_xdp(struct cpsw_priv *priv, int ch, struct xdp_buff *xdp,
> > +			struct page *page)
> > +{
> > +	struct cpsw_common *cpsw = priv->cpsw;
> > +	struct net_device *ndev = priv->ndev;
> > +	int ret = CPSW_XDP_CONSUMED;
> > +	struct xdp_frame *xdpf;
> > +	struct bpf_prog *prog;
> > +	u32 act;
> > +
> > +	rcu_read_lock();
> > +
> > +	prog = READ_ONCE(priv->xdp_prog);
> > +	if (!prog) {
> > +		ret = CPSW_XDP_PASS;
> > +		goto out;
> > +	}
> > +
> > +	act = bpf_prog_run_xdp(prog, xdp);
> > +	switch (act) {
> > +	case XDP_PASS:
> > +		ret = CPSW_XDP_PASS;
> > +		break;
> > +	case XDP_TX:
> > +		xdpf = convert_to_xdp_frame(xdp);
> > +		if (unlikely(!xdpf))
> > +			goto drop;
> > +
> > +		cpsw_xdp_tx_frame(priv, xdpf, page);
> > +		break;
> > +	case XDP_REDIRECT:
> > +		if (xdp_do_redirect(ndev, xdp, prog))
> > +			goto drop;
> > +
> > +		/* as flush requires rx_dev to be per NAPI handle and there
> > +		 * is can be two devices putting packets on bulk queue,
> > +		 * do flush here avoid this just for sure.
> > +		 */
> > +		xdp_do_flush_map();
>
> > +		break;
> > +	default:
> > +		bpf_warn_invalid_xdp_action(act);
> > +		/* fall through */
> > +	case XDP_ABORTED:
> > +		trace_xdp_exception(ndev, prog, act);
> > +		/* fall through -- handle aborts by dropping packet */
> > +	case XDP_DROP:
> > +		goto drop;
> > +	}
> > +out:
> > +	rcu_read_unlock();
> > +	return ret;
> > +drop:
> > +	rcu_read_unlock();
> > +	page_pool_recycle_direct(cpsw->page_pool[ch], page);
> > +	return ret;
> > +}
>
> --
> Best regards,
>  Jesper Dangaard Brouer
>  MSc.CS, Principal Kernel Engineer at Red Hat
>  LinkedIn: http://www.linkedin.com/in/brouer

--
Regards,
Ivan Khoronzhuk