Re: [PATCH RFC 1/2] can: Limit default size of CAN_RAW socket send queue

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 01/16/2014 08:58 PM, Michal Sojka wrote:
> This fixes the infamous ENOBUFS problem, which appears when an
> application sends CAN frames faster than they leave the system.
> 
> Packets for sending can be queued at three places: socket, queueing
> discipline and device driver. Only the socket queue is able to block
> the sender; other queues are non-blocking. Since the size of the qdisc
> queue was set by default to 10 packets, this queue was full much
> earlier than the socket queue and this resulted in ENOBUFS error.
> 
> This patch limits the default size of the socket send queue to
> approximately 3 CAN frames and increases the size of the qdisc queue
> to 100 frames. This setting allows for at least 33 CAN_RAW sockets to
> be used simultaneously in the system without getting ENOBUFS errors.

Do you mean in the system, per CAN interface or per socket? How many CAN
frames does a socket take before it blocks (with the default values), in
case the CAN interface doesn't send any messages?

> Note that the size of the socket queue is only approximate, because it
> is counted in bytes and the realy allocated memory (skb->truesize) can
> be bigger than what is reported by SKB_TRUESIZE(). For example, on my
> 32 bit PowerPC system, SKB_TRUESIZE() = 408, but skb->truesize = 448.

What does that mean for number of CAN frames in the above question?

> Open issues:
> - Will this work with CANFD?

Can you calculate the size in bytes depending if we have a CAN or a
CANFD network card at this socket?

> - What about other AF_CAN protocols?
> 
> Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>
> ---
>  drivers/net/can/dev.c | 2 +-
>  net/can/raw.c         | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
> index 1870c47..a0bce83 100644
> --- a/drivers/net/can/dev.c
> +++ b/drivers/net/can/dev.c
> @@ -492,7 +492,7 @@ static void can_setup(struct net_device *dev)
>  	dev->mtu = CAN_MTU;
>  	dev->hard_header_len = 0;
>  	dev->addr_len = 0;
> -	dev->tx_queue_len = 10;
> +	dev->tx_queue_len = 100;
>  
>  	/* New-style flags. */
>  	dev->flags = IFF_NOARP;
> diff --git a/net/can/raw.c b/net/can/raw.c
> index fdda5f6..4ad0bb2 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -291,6 +291,10 @@ static int raw_init(struct sock *sk)
>  {
>  	struct raw_sock *ro = raw_sk(sk);
>  
> +	/* allow at most 3 frames to wait for transmission in socket queue */
> +	sk->sk_sndbuf = 3 * SKB_TRUESIZE(sizeof(struct can_frame) +
> +					 sizeof(struct can_skb_priv));
> +
>  	ro->bound            = 0;
>  	ro->ifindex          = 0;
>  
> 

Marc
-- 
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