Subject: Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of traffic classes

From: Vinicius Costa Gomes <[email-masked]>
Date: Fri, 17 Jan 2020 16:03:07 -0800

Hi,

Po Liu <[email-masked]> writes:

> IEEE Std 802.1Qbu standard defined the frame preemption of port
> traffic classes. This patch introduce a method to set traffic
> classes preemption. Add a parameter 'preemption' in struct
> ethtool_link_settings. The value will be translated to a binary,
> each bit represent a traffic class. Bit "1" means preemptable
> traffic class. Bit "0" means express traffic class.  MSB represent
> high number traffic class.

I think that we should keep the concept of 'traffic classes' outside of
ethtool. Ethtool should only care about queues (or similar concepts).
And unless I am missing something here, what you mean by 'traffic class'
here is really a hardware queue.

>
> If hardware support the frame preemption, driver could set the
> ethernet device with hw_features and features with NETIF_F_PREEMPTION
> when initializing the port driver.
>
> User can check the feature 'tx-preemption' by command 'ethtool -k
> devname'. If hareware set preemption feature. The property would
> be a fixed value 'on' if hardware support the frame preemption.
> Feature would show a fixed value 'off' if hardware don't support
> the frame preemption.
>
> Command 'ethtool devname' and 'ethtool -s devname preemption N'
> would show/set which traffic classes are frame preemptable.
>
> Port driver would implement the frame preemption in the function
> get_link_ksettings() and set_link_ksettings() in the struct ethtool_ops.
>
> Signed-off-by: Po Liu <[email-masked]>
> ---
>  include/linux/netdev_features.h | 5 ++++-
>  include/uapi/linux/ethtool.h    | 5 ++++-
>  net/core/ethtool.c              | 1 +
>  3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
> index 4b19c544c59a..299750a8b414 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
> @@ -80,6 +80,7 @@ enum {
>  
>  	NETIF_F_GRO_HW_BIT,		/* Hardware Generic receive offload */
>  	NETIF_F_HW_TLS_RECORD_BIT,	/* Offload TLS record */
> +	NETIF_F_HW_PREEMPTION_BIT,	/* Hardware TC frame preemption */
>  
>  	/*
>  	 * Add your fresh new feature above and remember to update
> @@ -150,6 +151,7 @@ enum {
>  #define NETIF_F_GSO_UDP_L4	__NETIF_F(GSO_UDP_L4)
>  #define NETIF_F_HW_TLS_TX	__NETIF_F(HW_TLS_TX)
>  #define NETIF_F_HW_TLS_RX	__NETIF_F(HW_TLS_RX)
> +#define NETIF_F_PREEMPTION	__NETIF_F(HW_PREEMPTION)
>  
>  /* Finds the next feature with the highest number of the range of start till 0.
>   */
> @@ -175,7 +177,8 @@ static inline int find_next_netdev_feature(u64 feature, unsigned long start)
>  /* Features valid for ethtool to change */
>  /* = all defined minus driver/device-class-related */
>  #define NETIF_F_NEVER_CHANGE	(NETIF_F_VLAN_CHALLENGED | \
> -				 NETIF_F_LLTX | NETIF_F_NETNS_LOCAL)
> +				 NETIF_F_LLTX | NETIF_F_NETNS_LOCAL | \
> +				 NETIF_F_PREEMPTION)
>  
>  /* remember that ((t)1 << t_BITS) is undefined in C99 */
>  #define NETIF_F_ETHTOOL_BITS	((__NETIF_F_BIT(NETDEV_FEATURE_COUNT - 1) | \
> diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
> index d4591792f0b4..12ffb34afbfa 100644
> --- a/include/uapi/linux/ethtool.h
> +++ b/include/uapi/linux/ethtool.h
> @@ -1776,6 +1776,8 @@ enum ethtool_reset_flags {
>  };
>  #define ETH_RESET_SHARED_SHIFT	16
>  
> +/* Disable preemtion. */
> +#define PREEMPTION_DISABLE     0x0
>  
>  /**
>   * struct ethtool_link_settings - link control and status
> @@ -1886,7 +1888,8 @@ struct ethtool_link_settings {
>  	__s8	link_mode_masks_nwords;
>  	__u8	transceiver;
>  	__u8	reserved1[3];
> -	__u32	reserved[7];
> +	__u32	preemption;
> +	__u32	reserved[6];
>  	__u32	link_mode_masks[0];
>  	/* layout of link_mode_masks fields:
>  	 * __u32 map_supported[link_mode_masks_nwords];
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index cd9bc67381b2..6ffcd8a602b8 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -111,6 +111,7 @@ static const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN]
>  	[NETIF_F_HW_TLS_RECORD_BIT] =	"tls-hw-record",
>  	[NETIF_F_HW_TLS_TX_BIT] =	 "tls-hw-tx-offload",
>  	[NETIF_F_HW_TLS_RX_BIT] =	 "tls-hw-rx-offload",
> +	[NETIF_F_HW_PREEMPTION_BIT] =	 "tx-preemption",
>  };
>  
>  static const char
> -- 
> 2.17.1