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    SubjectRe: [PATCH net-next] tuntap: introduce tx skb ring
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    On 2016年05月16日 11:56, Eric Dumazet wrote:
    > 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)
    >

    Yes, this sounds good.

    > 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.

    Right, no need. But for tun_peek() we need spin_lock_bh() since it was
    called by vhost-net.

    Thanks

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