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

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Date:   Fri, 20 Apr 2018 11:04:36 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-remoteproc@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] virtio_ring: switch to dma_XX barriers for rpmsg



On 2018年04月20日 01:35, Michael S. Tsirkin wrote:
> 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,

Acked-by: Jason Wang <jasowang@...hat.com>