From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths. Date: Fri, 05 Sep 2014 12:25:40 +0930 Message-ID: <87egvqkc7n.fsf@rustcorp.com.au> References: <1409718556-3041-1-git-send-email-rusty@rustcorp.com.au> <1409718556-3041-4-git-send-email-rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Andy Lutomirski Cc: netdev , Linux Virtualization , "Michael S. Tsirkin" List-Id: virtualization@lists.linuxfoundation.org Andy Lutomirski writes: > On Tue, Sep 2, 2014 at 9:29 PM, Rusty Russell wrote: >> virtqueue_add() populates the virtqueue descriptor table from the sgs >> given. If it uses an indirect descriptor table, then it puts a single >> descriptor in the descriptor table pointing to the kmalloc'ed indirect >> table where the sg is populated. >> >> Previously vring_add_indirect() did the allocation and the simple >> linear layout. We replace that with alloc_indirect() which allocates >> the indirect table then chains it like the normal descriptor table so >> we can reuse the core logic. >> > >> + if (vq->indirect && total_sg > 1 && vq->vq.num_free) >> + desc = alloc_indirect(total_sg, gfp); >> + else >> + desc = NULL; >> + >> + if (desc) { >> + /* Use a single buffer which doesn't continue */ >> + vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT; >> + vq->vring.desc[head].addr = virt_to_phys(desc); >> + /* avoid kmemleak false positive (hidden by virt_to_phys) */ >> + kmemleak_ignore(desc); >> + vq->vring.desc[head].len = total_sg * sizeof(struct vring_desc); >> + >> + /* Set up rest to use this indirect table. */ >> + i = 0; >> + total_sg = 1; > > This is a little too magical for me. Would it make sense to add a new > variable for this (total_root_descs or something)? Agreed, it's a little hacky. Here's the diff (I actually merged this into the patch, but no point re-xmitting): diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index a4ebbffac141..6d2b5310c991 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -131,7 +131,7 @@ static inline int virtqueue_add(struct virtqueue *_vq, struct vring_virtqueue *vq = to_vvq(_vq); struct scatterlist *sg; struct vring_desc *desc; - unsigned int i, n, avail, uninitialized_var(prev); + unsigned int i, n, avail, descs_used, uninitialized_var(prev); int head; bool indirect; @@ -179,17 +179,18 @@ static inline int virtqueue_add(struct virtqueue *_vq, /* Set up rest to use this indirect table. */ i = 0; - total_sg = 1; + descs_used = 1; indirect = true; } else { desc = vq->vring.desc; i = head; + descs_used = total_sg; indirect = false; } - if (vq->vq.num_free < total_sg) { + if (vq->vq.num_free < descs_used) { pr_debug("Can't add buf len %i - avail = %i\n", - total_sg, vq->vq.num_free); + descs_used, vq->vq.num_free); /* FIXME: for historical reasons, we force a notify here if * there are outgoing parts to the buffer. Presumably the * host should service the ring ASAP. */ @@ -200,7 +201,7 @@ static inline int virtqueue_add(struct virtqueue *_vq, } /* We're about to use some buffers from the free list. */ - vq->vq.num_free -= total_sg; + vq->vq.num_free -= descs_used; for (n = 0; n < out_sgs; n++) { for (sg = sgs[n]; sg; sg = sg_next(sg)) {