netdev - Re: [PATCH net-next v1 1/9] ethtool: Add support for configuring frame preemption

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Message-ID: <20201205094325.790b187f@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Sat, 5 Dec 2020 09:43:25 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, m-karicheri2@...com, vladimir.oltean@....com,
        Jose.Abreu@...opsys.com, po.liu@....com,
        intel-wired-lan@...ts.osuosl.org, anthony.l.nguyen@...el.com
Subject: Re: [PATCH net-next v1 1/9] ethtool: Add support for configuring
 frame preemption

On Tue,  1 Dec 2020 20:53:17 -0800 Vinicius Costa Gomes wrote:
> Frame preemption (described in IEEE 802.3br-2016) defines the concept
> of preemptible and express queues. It allows traffic from express
> queues to "interrupt" traffic from preemptible queues, which are
> "resumed" after the express traffic has finished transmitting.
> 
> Frame preemption can only be used when both the local device and the
> link partner support it.
> 
> Only parameters for enabling/disabling frame preemption and
> configuring the minimum fragment size are included here. Expressing
> which queues are marked as preemptible is left to mqprio/taprio, as
> having that information there should be easier on the user.
> 
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> ---
>  include/linux/ethtool.h              |  19 ++++
>  include/uapi/linux/ethtool_netlink.h |  17 +++
>  net/ethtool/Makefile                 |   2 +-
>  net/ethtool/netlink.c                |  19 ++++
>  net/ethtool/netlink.h                |   4 +
>  net/ethtool/preempt.c                | 151 +++++++++++++++++++++++++++
>  6 files changed, 211 insertions(+), 1 deletion(-)
>  create mode 100644 net/ethtool/preempt.c
> 
> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
> index e3da25b51ae4..16d6ee29a6ac 100644
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -263,6 +263,19 @@ struct ethtool_pause_stats {
>  	u64 rx_pause_frames;
>  };
>  
> +/**
> + * struct ethtool_fp - Frame Preemption information
> + *
> + * @enabled: Enable frame preemption.
> + *

The empty line between members seems unnecessary.

> + * @min_frag_size_mult: Minimum size for all non-final fragment size,
> + * expressed in terms of X in '(1 + X)*64 + 4'

Is this way of expressing the min frag size from the standard?

> + */
> +struct ethtool_fp {
> +	u8 enabled;
> +	u8 min_frag_size_mult;
> +};

> +	int	(*get_preempt)(struct net_device *,
> +			       struct ethtool_fp *);
> +	int	(*set_preempt)(struct net_device *,
> +			       struct ethtool_fp *);

Since this is a new op we should probably pass extack to the drivers?

>  extern const struct nla_policy ethnl_header_policy[ETHTOOL_A_HEADER_FLAGS + 1];
>  extern const struct nla_policy ethnl_header_policy_stats[ETHTOOL_A_HEADER_FLAGS + 1];
> @@ -375,6 +376,8 @@ extern const struct nla_policy ethnl_tsinfo_get_policy[ETHTOOL_A_TSINFO_HEADER +
>  extern const struct nla_policy ethnl_cable_test_act_policy[ETHTOOL_A_CABLE_TEST_HEADER + 1];
>  extern const struct nla_policy ethnl_cable_test_tdr_act_policy[ETHTOOL_A_CABLE_TEST_TDR_CFG + 1];
>  extern const struct nla_policy ethnl_tunnel_info_get_policy[ETHTOOL_A_TUNNEL_INFO_HEADER + 1];
> +extern const struct nla_policy ethnl_preempt_get_policy[ETHTOOL_A_PREEMPT_MAX + 1];
> +extern const struct nla_policy ethnl_preempt_set_policy[ETHTOOL_A_PREEMPT_MAX + 1];

Let's make the size

ETHTOOL_A_PREEMPT_MIN_FRAG_SIZE_MULT + 1

for set, and

ETHTOOL_A_PREEMPT_HEADER + 1

for get, like the other tables

> +const struct nla_policy
> +ethnl_preempt_get_policy[ETHTOOL_A_PREEMPT_MAX + 1] = {
> +	[ETHTOOL_A_PREEMPT_UNSPEC]		= { .type = NLA_REJECT },

Unnecessary, NLA_REJECT is 0.

> +	[ETHTOOL_A_PREEMPT_HEADER]		= { .type = NLA_NESTED },

Please specify nested policy

> +	[ETHTOOL_A_PREEMPT_ENABLED]		= { .type = NLA_REJECT },
> +	[ETHTOOL_A_PREEMPT_MIN_FRAG_SIZE_MULT]	= { .type = NLA_REJECT },

Unnecessary

> +const struct nla_policy
> +ethnl_preempt_set_policy[ETHTOOL_A_PREEMPT_MAX + 1] = {
> +	[ETHTOOL_A_PREEMPT_UNSPEC]			= { .type = NLA_REJECT },
> +	[ETHTOOL_A_PREEMPT_HEADER]			= { .type = NLA_NESTED },
> +	[ETHTOOL_A_PREEMPT_ENABLED]			= { .type = NLA_U8 },

Set the right netlink policy to check the value is <= 1.

> +	[ETHTOOL_A_PREEMPT_MIN_FRAG_SIZE_MULT]		= { .type = NLA_U8 },
> +};