From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH 29/34] Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb" Date: Wed, 30 Dec 2015 15:26:18 +0200 Message-ID: <1451473761-30019-30-git-send-email-mst@redhat.com> References: <1451473761-30019-1-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1451473761-30019-1-git-send-email-mst@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Arnd Bergmann , linux-arch@vger.kernel.org, Andrew Cooper , virtualization@lists.linux-foundation.org, Stefano Stabellini , Alexander Duyck List-Id: linux-arch.vger.kernel.org This reverts commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9. While that commit optimizes !CONFIG_SMP, it mixes up DMA and SMP concepts, making the code hard to figure out. A better way to optimize this is with the new __smp_XXX barriers. As a first step, go back to full rmb/wmb barriers for !SMP. We switch to __smp_XXX barriers in the next patch. Cc: Peter Zijlstra Cc: Alexander Duyck Signed-off-by: Michael S. Tsirkin --- include/linux/virtio_ring.h | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 8e50888..67e06fe 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -21,20 +21,19 @@ * actually quite cheap. */ +#ifdef CONFIG_SMP static inline void virtio_mb(bool weak_barriers) { -#ifdef CONFIG_SMP if (weak_barriers) smp_mb(); else -#endif mb(); } static inline void virtio_rmb(bool weak_barriers) { if (weak_barriers) - dma_rmb(); + smp_rmb(); else rmb(); } @@ -42,10 +41,26 @@ static inline void virtio_rmb(bool weak_barriers) static inline void virtio_wmb(bool weak_barriers) { if (weak_barriers) - dma_wmb(); + smp_wmb(); else wmb(); } +#else +static inline void virtio_mb(bool weak_barriers) +{ + mb(); +} + +static inline void virtio_rmb(bool weak_barriers) +{ + rmb(); +} + +static inline void virtio_wmb(bool weak_barriers) +{ + wmb(); +} +#endif struct virtio_device; struct virtqueue; -- MST