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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
