lguest: suppress notifications in example Launcher (b60da13f) · Commits · 戴 / test

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>

Documentation/lguest/lguest.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -172,6 +172,7 @@ static struct termios orig_term;
		* threads and so we need to make sure that changes visible to the Guest happen
		* in precise order. */
		#define wmb() __asm__ __volatile__("" : : : "memory")
		#define mb() __asm__ __volatile__("" : : : "memory")

		/* Convert an iovec element to the given type.
		*
		@@ -593,9 +594,23 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq,
		/* OK, tell Guest about progress up to now. */
		trigger_irq(vq);

		/* OK, now we need to know about added descriptors. */
		vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;

		/* They could have slipped one in as we were doing that: make
		* sure it's written, then check again. */
		mb();
		if (last_avail != vq->vring.avail->idx) {
		vq->vring.used->flags \|= VRING_USED_F_NO_NOTIFY;
		break;
		}

		/* Nothing new? Wait for eventfd to tell us they refilled. */
		if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event))
		errx(1, "Event read failed?");

		/* We don't need to be notified again. */
		vq->vring.used->flags \|= VRING_USED_F_NO_NOTIFY;
		}

		/* Check it isn't doing very strange things with descriptor numbers. */

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