linux-kernel - [PATCH] virtio_ring: switch to dma

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Date:   Thu, 19 Apr 2018 20:35:57 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-remoteproc@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH] virtio_ring: switch to dma_XX barriers for rpmsg

virtio is using barriers to order memory accesses, thus
dma_wmb/rmb is a good match.

Build-tested on x86: Before

[mst@...k linux]$ size drivers/virtio/virtio_ring.o
   text    data     bss     dec     hex filename
  11392     820       0   12212    2fb4 drivers/virtio/virtio_ring.o

After
mst@...k linux]$ size drivers/virtio/virtio_ring.o
   text    data     bss     dec     hex filename
  11284     820       0   12104    2f48 drivers/virtio/virtio_ring.o

Cc: Ohad Ben-Cohen <ohad@...ery.com>
Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: linux-remoteproc@...r.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---

It's good in theory, but could one of RPMSG maintainers please review
and ack this patch? Or even better test it?

All these barriers are useless on Intel anyway ...

 include/linux/virtio_ring.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index bbf3252..fab0213 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -35,7 +35,7 @@ static inline void virtio_rmb(bool weak_barriers)
 	if (weak_barriers)
 		virt_rmb();
 	else
-		rmb();
+		dma_rmb();
 }
 
 static inline void virtio_wmb(bool weak_barriers)
@@ -43,7 +43,7 @@ static inline void virtio_wmb(bool weak_barriers)
 	if (weak_barriers)
 		virt_wmb();
 	else
-		wmb();
+		dma_wmb();
 }
 
 static inline void virtio_store_mb(bool weak_barriers,
-- 
MST