linux-kernel - Re: [PATCH] can: enable multi-queue for SocketCAN devices

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Date:   Wed, 14 Mar 2018 12:11:27 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Mark Jonas <mark.jonas@...bosch.com>,
        Wolfgang Grandegger <wg@...ndegger.com>
Cc:     linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, hs@...x.de,
        Zhu Yi <yi.zhu5@...bosch.com>
Subject: Re: [PATCH] can: enable multi-queue for SocketCAN devices

On 03/14/2018 11:33 AM, Mark Jonas wrote:
> From: Zhu Yi <yi.zhu5@...bosch.com>
> 
> The existing SocketCAN implementation provides alloc_candev() to
> allocate a CAN device using a single Tx and Rx queue. This can lead to
> priority inversion in case the single Tx queue is already full with low
> priority messages and a high priority message needs to be sent while the
> bus is fully loaded with medium priority messages.
> 
> This problem can be solved by using the existing multi-queue support of
> the network subsystem. The commit makes it possible to use multi-queue in
> the CAN subsystem in the same way it is used in the Ethernet subsystem
> by adding an alloc_candev_mqs() call and accompanying macros. With this
> support a CAN device can use multi-queue qdisc (e.g. mqprio) to avoid
> the aforementioned priority inversion.
> 
> The existing functionality of alloc_candev() is the same as before.
> 
> CAN devices need to have prioritized multiple hardware queues or are
> able to abort waiting for arbitration to make sensible use of
> multi-queues.
> 
> Signed-off-by: Zhu Yi <yi.zhu5@...bosch.com>
> Signed-off-by: Mark Jonas <mark.jonas@...bosch.com>
> Reviewed-by: Heiko Schocher <hs@...x.de>

Do you have a driver or a patch to make a driver mq aware?

> ---
>  drivers/net/can/dev.c   | 8 +++++---
>  include/linux/can/dev.h | 7 ++++++-
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
> index b177956..636f853 100644
> --- a/drivers/net/can/dev.c
> +++ b/drivers/net/can/dev.c
> @@ -703,7 +703,8 @@ EXPORT_SYMBOL_GPL(alloc_can_err_skb);
>  /*
>   * Allocate and setup space for the CAN network device
>   */
> -struct net_device *alloc_candev(int sizeof_priv, unsigned int echo_skb_max)
> +struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max,
> +				    unsigned int txqs, unsigned int rxqs)
>  {
>  	struct net_device *dev;
>  	struct can_priv *priv;
> @@ -715,7 +716,8 @@ struct net_device *alloc_candev(int sizeof_priv, unsigned int echo_skb_max)
>  	else
>  		size = sizeof_priv;
>  
> -	dev = alloc_netdev(size, "can%d", NET_NAME_UNKNOWN, can_setup);
> +	dev = alloc_netdev_mqs(size, "can%d", NET_NAME_UNKNOWN, can_setup,
> +			       txqs, rxqs);
>  	if (!dev)
>  		return NULL;
>  
> @@ -734,7 +736,7 @@ struct net_device *alloc_candev(int sizeof_priv, unsigned int echo_skb_max)
>  
>  	return dev;
>  }
> -EXPORT_SYMBOL_GPL(alloc_candev);
> +EXPORT_SYMBOL_GPL(alloc_candev_mqs);
>  
>  /*
>   * Free space of the CAN network device
> diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
> index 055aaf5..a83e1f6 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -143,7 +143,12 @@ u8 can_dlc2len(u8 can_dlc);
>  /* map the sanitized data length to an appropriate data length code */
>  u8 can_len2dlc(u8 len);
>  
> -struct net_device *alloc_candev(int sizeof_priv, unsigned int echo_skb_max);
> +struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max,
> +				    unsigned int txqs, unsigned int rxqs);
> +#define alloc_candev(sizeof_priv, echo_skb_max) \
> +	alloc_candev_mqs(sizeof_priv, echo_skb_max, 1, 1)
> +#define alloc_candev_mq(sizeof_priv, echo_skb_max, count) \
> +	alloc_candev_mqs(sizeof_priv, echo_skb_max, count, count)

Can you make this a static inline function.

>  void free_candev(struct net_device *dev);
>  
>  /* a candev safe wrapper around netdev_priv */
> 

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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