netdev - Re: [PATCH net-next] tuntap: introduce tx skb ring

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Message-ID: <1463370998.18194.74.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Sun, 15 May 2016 20:56:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring

On Mon, 2016-05-16 at 09:17 +0800, Jason Wang wrote:
> We used to queue tx packets in sk_receive_queue, this is less
> efficient since it requires spinlocks to synchronize between producer
> and consumer.

...

>  	struct tun_struct *detached;
> +	/* reader lock */
> +	spinlock_t rlock;
> +	unsigned long tail;
> +	struct tun_desc tx_descs[TUN_RING_SIZE];
> +	/* writer lock */
> +	spinlock_t wlock;
> +	unsigned long head;
>  };
>  

Ok, we had these kind of ideas floating around for many other cases,
like qdisc, UDP or af_packet sockets...

I believe we should have a common set of helpers, not hidden in
drivers/net/tun.c but in net/core/skb_ring.c or something, with more
flexibility (like the number of slots)


BTW, why are you using spin_lock_irqsave() in tun_net_xmit() and
tun_peek() ?

BH should be disabled already (in tun_next_xmit()), and we can not
transmit from hard irq.

Thanks.