Re: [PATCH v2 6/6] net: ocelot: add jumbo frame support for FDMA

[Clément Léger]

Le Wed, 3 Nov 2021 12:43:20 +0000,
Vladimir Oltean <vladimir.oltean@xxxxxxx> a écrit :

> On Wed, Nov 03, 2021 at 10:19:43AM +0100, Clément Léger wrote:
> > When using the FDMA, using jumbo frames can lead to a large performance
> > improvement. When changing the MTU, the RX buffer size must be
> > increased to be large enough to receive jumbo frame. Since the FDMA is
> > shared amongst all interfaces, all the ports must be down before
> > changing the MTU. Buffers are sized to accept the maximum MTU supported
> > by each port.
> > 
> > Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
> > ---  
> 
> Instead of draining buffers and refilling with a different size, which
> impacts the user experience, can you not just use scatter/gather RX
> processing for frames larger than the fixed buffer size, like a normal
> driver would?

I could do that yes but I'm not sure it will improve the FDMA
performance that much then. I will check.

> 
> >  drivers/net/ethernet/mscc/ocelot_fdma.c | 61 +++++++++++++++++++++++++
> >  drivers/net/ethernet/mscc/ocelot_fdma.h |  1 +
> >  drivers/net/ethernet/mscc/ocelot_net.c  |  7 +++
> >  3 files changed, 69 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/mscc/ocelot_fdma.c b/drivers/net/ethernet/mscc/ocelot_fdma.c
> > index d8cdf022bbee..bee1a310caa6 100644
> > --- a/drivers/net/ethernet/mscc/ocelot_fdma.c
> > +++ b/drivers/net/ethernet/mscc/ocelot_fdma.c
> > @@ -530,6 +530,67 @@ static void fdma_free_skbs_list(struct ocelot_fdma *fdma,
> >  	}
> >  }
> >  
> > +int ocelot_fdma_change_mtu(struct net_device *dev, int new_mtu)
> > +{
> > +	struct ocelot_port_private *priv = netdev_priv(dev);
> > +	struct ocelot_port *port = &priv->port;
> > +	struct ocelot *ocelot = port->ocelot;
> > +	struct ocelot_fdma *fdma = ocelot->fdma;
> > +	struct ocelot_fdma_dcb *dcb, *dcb_temp;
> > +	struct list_head tmp = LIST_HEAD_INIT(tmp);
> > +	size_t old_rx_buf_size = fdma->rx_buf_size;
> > +	bool all_ports_down = true;
> > +	u8 port_num;
> > +
> > +	/* The FDMA RX list is shared amongst all the port, get the max MTU from
> > +	 * all of them
> > +	 */
> > +	for (port_num = 0; port_num < ocelot->num_phys_ports; port_num++) {
> > +		port = ocelot->ports[port_num];
> > +		if (!port)
> > +			continue;
> > +
> > +		priv = container_of(port, struct ocelot_port_private, port);
> > +
> > +		if (READ_ONCE(priv->dev->mtu) > new_mtu)
> > +			new_mtu = READ_ONCE(priv->dev->mtu);
> > +
> > +		/* All ports must be down to change the RX buffer length */
> > +		if (netif_running(priv->dev))
> > +			all_ports_down = false;
> > +	}
> > +
> > +	fdma->rx_buf_size = fdma_rx_compute_buffer_size(new_mtu);
> > +	if (fdma->rx_buf_size == old_rx_buf_size)
> > +		return 0;
> > +
> > +	if (!all_ports_down)
> > +		return -EBUSY;
> > +
> > +	priv = netdev_priv(dev);
> > +
> > +	fdma_stop_channel(fdma, MSCC_FDMA_INJ_CHAN);
> > +
> > +	/* Discard all pending RX software and hardware descriptor */
> > +	fdma_free_skbs_list(fdma, &fdma->rx_hw, DMA_FROM_DEVICE);
> > +	fdma_free_skbs_list(fdma, &fdma->rx_sw, DMA_FROM_DEVICE);
> > +
> > +	/* Move all DCBs to a temporary list that will be injected in sw list */
> > +	if (!list_empty(&fdma->rx_hw))
> > +		list_splice_tail_init(&fdma->rx_hw, &tmp);
> > +	if (!list_empty(&fdma->rx_sw))
> > +		list_splice_tail_init(&fdma->rx_sw, &tmp);
> > +
> > +	list_for_each_entry_safe(dcb, dcb_temp, &tmp, node) {
> > +		list_del(&dcb->node);
> > +		ocelot_fdma_rx_add_dcb_sw(fdma, dcb);
> > +	}
> > +
> > +	ocelot_fdma_rx_refill(fdma);
> > +
> > +	return 0;
> > +}
> > +
> >  static int fdma_init_tx(struct ocelot_fdma *fdma)
> >  {
> >  	int i;
> > diff --git a/drivers/net/ethernet/mscc/ocelot_fdma.h b/drivers/net/ethernet/mscc/ocelot_fdma.h
> > index 6c5c5872abf5..74514a0b291a 100644
> > --- a/drivers/net/ethernet/mscc/ocelot_fdma.h
> > +++ b/drivers/net/ethernet/mscc/ocelot_fdma.h
> > @@ -55,5 +55,6 @@ int ocelot_fdma_start(struct ocelot_fdma *fdma);
> >  int ocelot_fdma_stop(struct ocelot_fdma *fdma);
> >  int ocelot_fdma_inject_frame(struct ocelot_fdma *fdma, int port, u32 rew_op,
> >  			     struct sk_buff *skb, struct net_device *dev);
> > +int ocelot_fdma_change_mtu(struct net_device *dev, int new_mtu);
> >  
> >  #endif
> > diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
> > index 3971b810c5b4..d5e88d7b15c7 100644
> > --- a/drivers/net/ethernet/mscc/ocelot_net.c
> > +++ b/drivers/net/ethernet/mscc/ocelot_net.c
> > @@ -492,6 +492,13 @@ static int ocelot_change_mtu(struct net_device *dev, int new_mtu)
> >  	struct ocelot_port_private *priv = netdev_priv(dev);
> >  	struct ocelot_port *ocelot_port = &priv->port;
> >  	struct ocelot *ocelot = ocelot_port->ocelot;
> > +	int ret;
> > +
> > +	if (ocelot->fdma) {
> > +		ret = ocelot_fdma_change_mtu(dev, new_mtu);
> > +		if (ret)
> > +			return ret;
> > +	}
> >  
> >  	ocelot_port_set_maxlen(ocelot, priv->chip_port, new_mtu);
> >  	WRITE_ONCE(dev->mtu, new_mtu);
> > -- 
> > 2.33.0
>   



-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com