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| author | Rusty Russell <rusty@rustcorp.com.au> | 2009-06-12 22:27:12 -0600 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2009-06-12 22:27:13 +0930 |
| commit | b60da13fc7bbf99d3c68578bd3fbcf66e1cb5f41 (patch) | |
| tree | 6ae96583da3212755d867fdff30b2f9ae58609e8 /Documentation/lguest | |
| parent | 4a8962e21bc505c714fc2508494d4c7dd3fe2d29 (diff) | |
| download | lwn-b60da13fc7bbf99d3c68578bd3fbcf66e1cb5f41.tar.gz lwn-b60da13fc7bbf99d3c68578bd3fbcf66e1cb5f41.zip | |
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>
Diffstat (limited to 'Documentation/lguest')
| -rw-r--r-- | Documentation/lguest/lguest.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c index 64110797044a..bb5e3c28d9d6 100644 --- a/Documentation/lguest/lguest.c +++ b/Documentation/lguest/lguest.c @@ -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. */ |