Christian Borntraeger wrote:
Am Dienstag, 11. Dezember 2007 schrieb Christian Borntraeger:
The way other physical NICs doing it is by dis/en/abling interrupt
using registers (look at e1000).
I suggest we can export add_status and use the original code but
before enabling napi add a call to add_status(dev,
VIRTIO_CONFIG_DEV_OPEN).
The host won't trigger an irq until it sees the above.
That would also work. We already have VRING_AVAIL_F_NO_INTERRUPT in
virtio_ring.c - maybe we can use that. Its hidden in callback and
restart handling, what about adding an explicit startup?
Ok, just to give an example what I thought about:
---
drivers/block/virtio_blk.c | 3 ++-
drivers/net/virtio_net.c | 2 ++
drivers/virtio/virtio_ring.c | 16 +++++++++++++---
include/linux/virtio.h | 5 +++++
4 files changed, 22 insertions(+), 4 deletions(-)
Index: kvm/drivers/virtio/virtio_ring.c
===================================================================
--- kvm.orig/drivers/virtio/virtio_ring.c
+++ kvm/drivers/virtio/virtio_ring.c
@@ -241,6 +241,16 @@ static bool vring_restart(struct virtque
return true;
}
+static void vring_startup(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ START_USE(vq);
+ if (vq->vq.callback)
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ END_USE(vq);
+}
+
+
irqreturn_t vring_interrupt(int irq, void *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -265,6 +275,7 @@ static struct virtqueue_ops vring_vq_ops
.get_buf = vring_get_buf,
.kick = vring_kick,
.restart = vring_restart,
+ .startup = vring_startup,
.shutdown = vring_shutdown,
};
@@ -299,9 +310,8 @@ struct virtqueue *vring_new_virtqueue(un
vq->in_use = false;
#endif
- /* No callback? Tell other side not to bother us. */
- if (!callback)
- vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
+ /* disable interrupts until we enable them */
+ vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
/* Put everything in free lists. */
vq->num_free = num;
Index: kvm/include/linux/virtio.h
===================================================================
--- kvm.orig/include/linux/virtio.h
+++ kvm/include/linux/virtio.h
@@ -45,6 +45,9 @@ struct virtqueue
* vq: the struct virtqueue we're talking about.
* This returns "false" (and doesn't re-enable) if there are pending
* buffers in the queue, to avoid a race.
+ * @startup: enable callbacks
+ * vq: the struct virtqueue we're talking abount
+ * Returns 0 or an error
* @shutdown: "unadd" all buffers.
* vq: the struct virtqueue we're talking about.
* Remove everything from the queue.
@@ -67,6 +70,8 @@ struct virtqueue_ops {
bool (*restart)(struct virtqueue *vq);
+ void (*startup) (struct virtqueue *vq);
+
void (*shutdown)(struct virtqueue *vq);
};
Index: kvm/drivers/net/virtio_net.c
===================================================================
--- kvm.orig/drivers/net/virtio_net.c
+++ kvm/drivers/net/virtio_net.c
@@ -292,6 +292,8 @@ static int virtnet_open(struct net_devic
return -ENOMEM;
napi_enable(&vi->napi);
+
+ vi->rvq->vq_ops->startup(vi->rvq);
return 0;
}
Index: kvm/drivers/block/virtio_blk.c
===================================================================
--- kvm.orig/drivers/block/virtio_blk.c
+++ kvm/drivers/block/virtio_blk.c
@@ -183,7 +183,8 @@ static int virtblk_probe(struct virtio_d
err = PTR_ERR(vblk->vq);
goto out_free_vblk;
}
-
+ /* enable interrupts */
+ vblk->vq->vq_ops->startup(vblk->vq);
vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
if (!vblk->pool) {
err = -ENOMEM;
There is still one small problem: what if the host fills up all
host-to-guest buffers before we call startup? So I start to think that your
solution is better, given that the host is not only not sending interrupts
This is why initially I suggested another status code in order to split
the ring logic with driver status.
but also not filling any buffers as long as VIRTIO_CONFIG_DEV_OPEN is not
set. I will have a look but I think that add_status needs to be called
It can fill the buffers even without dev_open, when the dev is finally
opened the host will issue an interrupt
if there are pending buffers. (I'm not sure it's worth solving, maybe
just drop them like you suggested).
after napi_enable, otherwise we have the same race.
You're right, my mistake.
Christian
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