Re: [PATCH v2 3/6] net: ocelot: pre-compute injection frame header content

Vladimir Oltean
2021-11-03T12:38:19Z

On Wed, Nov 03, 2021 at 10:19:40AM +0100, Clément Léger wrote:
> IFH preparation can take quite some time on slow processors (up to 5% in
> a iperf3 test for instance). In order to reduce the cost of this
> preparation, pre-compute IFH since most of the parameters are fixed per
> port. Only rew_op and vlan tag will be set when sending if different
> than 0. This allows to remove entirely the calls to packing() with basic
> usage. In the same time, export this function that will be used by FDMA.
>
> Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> ---

Honestly, this feels a bit cheap/gimmicky, and not really the
fundamental thing to address. In my testing of a similar idea (see
commits 67c2404922c2 ("net: dsa: felix: create a template for the DSA
tags on xmit") and then 7c4bb540e917 ("net: dsa: tag_ocelot: create
separate tagger for Seville"), the net difference is not that stark,
considering that now you need to access one more memory region which you
did not need before, do a memcpy, and then patch the IFH anyway for the
non-constant stuff.

Certainly, for the calls to ocelot_port_inject_frame() from DSA, I would
prefer not having this pre-computed IFH.

Could you provide some before/after performance numbers and perf counters?

> drivers/net/ethernet/mscc/ocelot.c | 23 ++++++++++++++++++-----
> include/soc/mscc/ocelot.h | 5 +++++
> 2 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index e6c18b598d5c..97693772595b 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -1076,20 +1076,29 @@ bool ocelot_can_inject(struct ocelot *ocelot, int grp)
> }
> EXPORT_SYMBOL(ocelot_can_inject);
>
> +void ocelot_ifh_port_set(void *ifh, struct ocelot_port *port, u32 rew_op,
> + u32 vlan_tag)
> +{
> + memcpy(ifh, port->ifh, OCELOT_TAG_LEN);
> +
> + if (vlan_tag)
> + ocelot_ifh_set_vlan_tci(ifh, vlan_tag);
> + if (rew_op)
> + ocelot_ifh_set_rew_op(ifh, rew_op);
> +}
> +EXPORT_SYMBOL(ocelot_ifh_port_set);
> +
> void ocelot_port_inject_frame(struct ocelot *ocelot, int port, int grp,
> u32 rew_op, struct sk_buff *skb)
> {
> + struct ocelot_port *port_s = ocelot->ports[port];
> u32 ifh[OCELOT_TAG_LEN / 4] = {0};
> unsigned int i, count, last;
>
> ocelot_write_rix(ocelot, QS_INJ_CTRL_GAP_SIZE(1) |
> QS_INJ_CTRL_SOF, QS_INJ_CTRL, grp);
>
> - ocelot_ifh_set_bypass(ifh, 1);
> - ocelot_ifh_set_dest(ifh, BIT_ULL(port));
> - ocelot_ifh_set_tag_type(ifh, IFH_TAG_TYPE_C);
> - ocelot_ifh_set_vlan_tci(ifh, skb_vlan_tag_get(skb));
> - ocelot_ifh_set_rew_op(ifh, rew_op);
> + ocelot_ifh_port_set(ifh, port_s, rew_op, skb_vlan_tag_get(skb));
>
> for (i = 0; i < OCELOT_TAG_LEN / 4; i++)
> ocelot_write_rix(ocelot, ifh[i], QS_INJ_WR, grp);
> @@ -2128,6 +2137,10 @@ void ocelot_init_port(struct ocelot *ocelot, int port)
>
> skb_queue_head_init(&ocelot_port->tx_skbs);
>
> + ocelot_ifh_set_bypass(ocelot_port->ifh, 1);
> + ocelot_ifh_set_dest(ocelot_port->ifh, BIT_ULL(port));
> + ocelot_ifh_set_tag_type(ocelot_port->ifh, IFH_TAG_TYPE_C);
> +
> /* Basic L2 initialization */
>
> /* Set MAC IFG Gaps
> diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
> index fef3a36b0210..b3381c90ff3e 100644
> --- a/include/soc/mscc/ocelot.h
> +++ b/include/soc/mscc/ocelot.h
> @@ -6,6 +6,7 @@
> #define _SOC_MSCC_OCELOT_H
>
> #include <linux/ptp_clock_kernel.h>
> +#include <linux/dsa/ocelot.h>
> #include <linux/net_tstamp.h>
> #include <linux/if_vlan.h>
> #include <linux/regmap.h>
> @@ -623,6 +624,8 @@ struct ocelot_port {
>
> struct net_device *bridge;
> u8 stp_state;
> +
> + u8 ifh[OCELOT_TAG_LEN];
> };
>
> struct ocelot {
> @@ -754,6 +757,8 @@ void __ocelot_target_write_ix(struct ocelot *ocelot, enum ocelot_target target,
> bool ocelot_can_inject(struct ocelot *ocelot, int grp);
> void ocelot_port_inject_frame(struct ocelot *ocelot, int port, int grp,
> u32 rew_op, struct sk_buff *skb);
> +void ocelot_ifh_port_set(void *ifh, struct ocelot_port *port, u32 rew_op,
> + u32 vlan_tag);
> int ocelot_xtr_poll_frame(struct ocelot *ocelot, int grp, struct sk_buff **skb);
> void ocelot_drain_cpu_queue(struct ocelot *ocelot, int grp);
>
> --
> 2.33.0
>