Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

On Sep 5, 2014 3:55 AM, "Paolo Bonzini" [off-list ref] wrote:

Il 03/09/2014 06:29, Rusty Russell ha scritto:

quoted

+     desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
+     if (!desc)
+             return NULL;

-     return head;
+     for (i = 0; i < total_sg; i++)
+             desc[i].next = i+1;
+     return desc;
 }

Would it make sense to keep a cache of a few (say) 8- or 16-element
indirect descriptors?  You'd only have to do this ugly (and slowish) for
loop on the first allocation.

Also, since this is mostly an aesthetic patch,

quoted

+     if (indirect)
+             vq->free_head = vq->vring.desc[head].next;
+     else
+             vq->free_head = i;

I'd move the indirect case above, where the vring.desc[head] is actually
allocated.

Please don't: I'll just have to undo it for the DMA API stuff, since
descriptor setup will be able to fail.

--Andy