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Date: Fri, 1 Jan 2016 12:21:52 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
Andrew Cooper <andrew.cooper3@...rix.com>,
virtualization@...ts.linux-foundation.org,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
adi-buildroot-devel@...ts.sourceforge.net,
linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
xen-devel@...ts.xenproject.org,
Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH v2 30/32] virtio_ring: update weak barriers to use
__smp_xxx
On Fri, Jan 01, 2016 at 11:39:40AM +0200, Michael S. Tsirkin wrote:
> virtio ring uses smp_wmb on SMP and wmb on !SMP,
> the reason for the later being that it might be
> talking to another kernel on the same SMP machine.
>
> This is exactly what __smp_XXX barriers do,
> so switch to these instead of homegrown ifdef hacks.
>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexander Duyck <alexander.duyck@...il.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
The subject and commit log should say
virt_xxx and not __smp_xxx - I fixed this up in
my tree.
> ---
> include/linux/virtio_ring.h | 25 ++++---------------------
> 1 file changed, 4 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> index 67e06fe..f3fa55b 100644
> --- a/include/linux/virtio_ring.h
> +++ b/include/linux/virtio_ring.h
> @@ -12,7 +12,7 @@
> * anyone care?
> *
> * For virtio_pci on SMP, we don't need to order with respect to MMIO
> - * accesses through relaxed memory I/O windows, so smp_mb() et al are
> + * accesses through relaxed memory I/O windows, so virt_mb() et al are
> * sufficient.
> *
> * For using virtio to talk to real devices (eg. other heterogeneous
> @@ -21,11 +21,10 @@
> * actually quite cheap.
> */
>
> -#ifdef CONFIG_SMP
> static inline void virtio_mb(bool weak_barriers)
> {
> if (weak_barriers)
> - smp_mb();
> + virt_mb();
> else
> mb();
> }
> @@ -33,7 +32,7 @@ static inline void virtio_mb(bool weak_barriers)
> static inline void virtio_rmb(bool weak_barriers)
> {
> if (weak_barriers)
> - smp_rmb();
> + virt_rmb();
> else
> rmb();
> }
> @@ -41,26 +40,10 @@ static inline void virtio_rmb(bool weak_barriers)
> static inline void virtio_wmb(bool weak_barriers)
> {
> if (weak_barriers)
> - smp_wmb();
> + virt_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
--
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