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

Clément Léger
2021-11-03T14:30:20Z

Le Wed, 3 Nov 2021 12:43:20 +0000,
Vladimir Oltean <vladimir.oltean@nxp.com> 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@bootlin.com>
> > ---
>
> 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