On Sun, 2011-12-04 at 19:39 +0200, Sasha Levin wrote:
> On Sun, 2011-12-04 at 19:37 +0200, Avi Kivity wrote:
> > On 12/04/2011 07:34 PM, Sasha Levin wrote:
> > > >
> > > > I'm confused. didn't you see a bigger benefit for guest->host by
> > > > switching indirect off?
> > >
> > > The 5% improvement is over the 'regular' indirect on, not over indirect
> > > off. Sorry for the confusion there.
> > >
> > > I suggested this change regardless of the outcome of indirect descriptor
> > > threshold discussion, since it would help anyways.
> >
> > For net, this makes sense. For block, it reduces the effective queue
> > depth, so it's not a trivial change. It probably makes sense there too,
> > though.
>
> It doesn't have to be limited at that number, anything above that can go
> through the regular kmalloc() path.
Something like the following patch:
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c7a2c20..3166ca0 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -82,6 +82,7 @@ struct vring_virtqueue
/* Host supports indirect buffers */
bool indirect;
+ struct kmem_cache *indirect_cache;
/* Host publishes avail event idx */
bool event;
@@ -110,6 +111,9 @@ struct vring_virtqueue
#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
+static unsigned int ind_alloc_thresh = 0;
+module_param(ind_alloc_thresh, uint, S_IRUGO);
+
/* Set up an indirect table of descriptors and add it to the queue. */
static int vring_add_indirect(struct vring_virtqueue *vq,
struct scatterlist sg[],
@@ -121,7 +125,10 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
unsigned head;
int i;
- desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
+ if ((out + in) <= ind_alloc_thresh)
+ desc = kmem_cache_alloc(vq->indirect_cache, gfp);
+ else
+ desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
if (!desc)
return -ENOMEM;
@@ -479,6 +486,9 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
vq->broken = false;
vq->last_used_idx = 0;
vq->num_added = 0;
+ if (ind_alloc_thresh)
+ vq->indirect_cache = KMEM_CACHE(vring_desc[ind_alloc_thresh],
0);
list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
vq->in_use = false;
--
Sasha.
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