Commit b60da13f authored by Rusty Russell's avatar Rusty Russell
Browse files

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

 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: default avatarRusty Russell <>
parent 4a8962e2
......@@ -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. */
/* 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. */
if (last_avail != vq->vring.avail->idx) {
vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
/* 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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