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lguest: suppress notifications in example Launcher
The Guest only really needs to tell us about activity when we're going to listen to the eventfd: normally, we don't want to know. So if there are no available buffers, turn on notifications, re-check, then wait for the Guest to notify us via the eventfd, then turn notifications off again. There's enough else going on that the differences are in the noise. Before: Secs RxKicks TxKicks 1G TCP Guest->Host: 3.94 4686 32815 1M normal pings: 104 142862 1000010 1M 1k pings (-l 120): 57 142026 1000007 After: 1G TCP Guest->Host: 3.76 4691 32811 1M normal pings: 111 142859 997467 1M 1k pings (-l 120): 55 19648 501549 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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1 changed files with 15 additions and 0 deletions
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@ -172,6 +172,7 @@ static struct termios orig_term;
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* threads and so we need to make sure that changes visible to the Guest happen
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* in precise order. */
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#define wmb() __asm__ __volatile__("" : : : "memory")
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#define mb() __asm__ __volatile__("" : : : "memory")
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/* Convert an iovec element to the given type.
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*
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@ -593,9 +594,23 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq,
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/* OK, tell Guest about progress up to now. */
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trigger_irq(vq);
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/* OK, now we need to know about added descriptors. */
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vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;
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/* They could have slipped one in as we were doing that: make
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* sure it's written, then check again. */
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mb();
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if (last_avail != vq->vring.avail->idx) {
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vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
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break;
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}
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/* Nothing new? Wait for eventfd to tell us they refilled. */
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if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event))
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errx(1, "Event read failed?");
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/* We don't need to be notified again. */
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vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
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}
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/* Check it isn't doing very strange things with descriptor numbers. */
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