Date: Thu, 13 Sep 2012 08:59:38 -0400 From: John Baldwin <jhb@freebsd.org> To: Peter Grehan <grehan@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r240427 - head/sys/dev/virtio Message-ID: <201209130859.38153.jhb@freebsd.org> In-Reply-To: <201209130036.q8D0aleB080371@svn.freebsd.org> References: <201209130036.q8D0aleB080371@svn.freebsd.org>
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On Wednesday, September 12, 2012 8:36:47 pm Peter Grehan wrote: > Author: grehan > Date: Thu Sep 13 00:36:46 2012 > New Revision: 240427 > URL: http://svn.freebsd.org/changeset/base/240427 > > Log: > Relax requirement of certain mb()s > > Submitted by: Bryan Venteicher bryanv at daemoninthecloset org > > Modified: > head/sys/dev/virtio/virtqueue.c > > Modified: head/sys/dev/virtio/virtqueue.c > ============================================================================== > --- head/sys/dev/virtio/virtqueue.c Wed Sep 12 22:54:11 2012 (r240426) > +++ head/sys/dev/virtio/virtqueue.c Thu Sep 13 00:36:46 2012 (r240427) > @@ -525,7 +525,7 @@ virtqueue_dequeue(struct virtqueue *vq, > used_idx = vq->vq_used_cons_idx++ & (vq->vq_nentries - 1); > uep = &vq->vq_ring.used->ring[used_idx]; > > - mb(); > + rmb(); > desc_idx = (uint16_t) uep->id; > if (len != NULL) > *len = uep->len; > @@ -623,7 +623,7 @@ vq_ring_update_avail(struct virtqueue *v > avail_idx = vq->vq_ring.avail->idx & (vq->vq_nentries - 1); > vq->vq_ring.avail->ring[avail_idx] = desc_idx; > > - mb(); > + wmb(); > vq->vq_ring.avail->idx++; > > /* Keep pending count until virtqueue_notify(). */ Would it be possible to use atomic_load/store() instead of direct memory barriers? For example: desc_idx = (uint16_t)atomic_load_acq_int(&uep->id); and atomic_store_rel_int(&vq->vq_ring.avail->ring[avail_idx], desc_idx); -- John Baldwin
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