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virtio: harsher barriers for rpmsg.

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We were cheating with our barriers; using the smp ones rather than the
real device ones.  That was fine, until rpmsg came along, which is
used to talk to a real device (a non-SMP CPU).

Unfortunately, just putting back the real barriers (reverting
d57ed95d) causes a performance regression on virtio-pci.  In
particular, Amos reports netbench's TCP_RR over virtio_net CPU
utilization increased up to 35% while throughput went down by up to
14%.

By comparison, this branch is in the noise.

Reference: https://lkml.org/lkml/2011/12/11/22

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2012-01-12 15:44:42 +10:30
parent e343a895a9
commit 7b21e34fd1
8 changed files with 35 additions and 22 deletions
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3
tools/virtio/virtio_test.c
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@ -92,7 +92,8 @@ static void vq_info_add(struct vdev_info *dev, int num)
assert(r >= 0);
memset(info->ring, 0, vring_size(num, 4096));
vring_init(&info->vring, num, info->ring, 4096);
info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev, info->ring,
info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev,
true, info->ring,
vq_notify, vq_callback, "test");
assert(info->vq);
info->vq->priv = info;