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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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drivers/virtio/virtio_pci.c
+2 -2
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@@ -414,8 +414,8 @@ static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index,
vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
/* create the vring */
vq = vring_new_virtqueue(info->num, VIRTIO_PCI_VRING_ALIGN,
vdev, info->queue, vp_notify, callback, name);
vq = vring_new_virtqueue(info->num, VIRTIO_PCI_VRING_ALIGN, vdev,
true, info->queue, vp_notify, callback, name);
if (!vq) {
err = -ENOMEM;
goto out_activate_queue;