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

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Date:   Wed, 3 Nov 2021 12:38:12 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Clément Léger <clement.leger@...tlin.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 3/6] net: ocelot: pre-compute injection frame header
 content

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@...tlin.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
>