On 30/07/14 20:50, Zoltan Kiss wrote:
> Currently when the guest is not able to receive more packets, qdisc layer
> starts
> a timer, and when it goes off, qdisc is started again to deliver a packet
> again.
> This is a very slow way to drain the queues, consumes unnecessary resources
> and
> slows down other guests shutdown.
> This patch change the behaviour by turning the carrier off when that timer
> fires, so all the packets are freed up which were stucked waiting for that
> vif.
> Instead of the rx_queue_purge bool it uses the VIF_STATUS_RX_PURGE_EVENT bit
> to
> signal the thread that either the timout happened or an RX interrupt arrived,
> so
> the thread can check what it should do. It also disables NAPI, so the guest
> can't transmit, but leaves the interrupts on, so it can resurrect.
I don't think you should disable NAPI, particularly since you have to
fiddle with the bits directly instead of usign the API to do so.
I looked at some hardware drivers and none of them disabled NAPI -- they
just allow it to naturally end once hardware queues are drained.
netback is a little different as a frontend could stop processing
to-guest packets but continue sending from-guest ones. I don't see any
problem with allowing this.
> @@ -1955,24 +1955,78 @@ int xenvif_kthread_guest_rx(void *data)
> */
> if (unlikely(queue->vif->disabled && queue->id == 0))
> xenvif_carrier_off(queue->vif);
> + else if
> (unlikely(test_and_clear_bit(QUEUE_STATUS_RX_PURGE_EVENT,
> + &queue->status))) {
> + /* Either the last unsuccesful skb or at least 1 slot
> + * should fit
> + */
> + int needed = queue->rx_last_skb_slots ?
> + queue->rx_last_skb_slots : 1;
>
> - if (kthread_should_stop())
> - break;
> -
> - if (queue->rx_queue_purge) {
> + /* It is assumed that if the guest post new
> + * slots after this, the RX interrupt will set
> + * the bit and wake up the thread again
> + */
> + set_bit(QUEUE_STATUS_RX_STALLED, &queue->status);
This big if needs to go in a new function.
David
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