From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH RFC 4/4] virtio: use dependent_ptr_mb Date: Wed, 2 Jan 2019 15:58:03 -0500 Message-ID: <20190102205715.14054-5-mst@redhat.com> References: <20190102205715.14054-1-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190102205715.14054-1-mst@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Jason Wang , Alan Stern , Andrea Parri , Will Deacon , Peter Zijlstra , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , Daniel Lustig , linux-arch@vger.kernel.org, netdev@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: linux-arch.vger.kernel.org Use dependent_ptr_mb which is - on some architectures - more light-weight than an rmb. Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 814b395007b2..2d320396eff8 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -702,6 +702,7 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len, void *ret; unsigned int i; u16 last_used; + bool more; START_USE(vq); @@ -710,14 +711,15 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len, return NULL; } - if (!more_used(vq)) { + more = more_used(vq); + if (!more) { pr_debug("No more buffers in queue\n"); END_USE(vq); return NULL; } /* Only get used array entries after they have been exposed by host. */ - virtio_rmb(vq->weak_barriers); + vq = dependent_ptr_mb(vq, more); last_used = (vq->last_used_idx & (vq->vring.num - 1)); i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id); -- MST From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:59918 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728953AbfABU6L (ORCPT ); Wed, 2 Jan 2019 15:58:11 -0500 Date: Wed, 2 Jan 2019 15:58:03 -0500 From: "Michael S. Tsirkin" Subject: [PATCH RFC 4/4] virtio: use dependent_ptr_mb Message-ID: <20190102205715.14054-5-mst@redhat.com> References: <20190102205715.14054-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190102205715.14054-1-mst@redhat.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: Jason Wang , Alan Stern , Andrea Parri , Will Deacon , Peter Zijlstra , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , Daniel Lustig , linux-arch@vger.kernel.org, netdev@vger.kernel.org, virtualization@lists.linux-foundation.org Message-ID: <20190102205803.w3oQQaQHqYYGILEQ1ZNahW57SYNiXjpH5eP_Rae-_4w@z> Use dependent_ptr_mb which is - on some architectures - more light-weight than an rmb. Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 814b395007b2..2d320396eff8 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -702,6 +702,7 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len, void *ret; unsigned int i; u16 last_used; + bool more; START_USE(vq); @@ -710,14 +711,15 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len, return NULL; } - if (!more_used(vq)) { + more = more_used(vq); + if (!more) { pr_debug("No more buffers in queue\n"); END_USE(vq); return NULL; } /* Only get used array entries after they have been exposed by host. */ - virtio_rmb(vq->weak_barriers); + vq = dependent_ptr_mb(vq, more); last_used = (vq->last_used_idx & (vq->vring.num - 1)); i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id); -- MST