From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Stabellini Subject: Re: [PATCH 32/34] xen/io: use __smp_XXX barriers Date: Mon, 4 Jan 2016 11:59:42 +0000 Message-ID: References: <1451473761-30019-1-git-send-email-mst@redhat.com> <1451473761-30019-33-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1451473761-30019-33-git-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: linux-arch@vger.kernel.org, Arnd Bergmann , Stefano Stabellini , Peter Zijlstra , Andrew Cooper , Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, David Vrabel , xen-devel@lists.xenproject.org, Boris Ostrovsky List-Id: linux-arch.vger.kernel.org On Wed, 30 Dec 2015, Michael S. Tsirkin wrote: > include/xen/interface/io/ring.h uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to __smp_XXX barriers which serve this exact purpose. > > Signed-off-by: Michael S. Tsirkin Reviewed-by: Stefano Stabellini > include/xen/interface/io/ring.h | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h > index 7dc685b..46dfc65 100644 > --- a/include/xen/interface/io/ring.h > +++ b/include/xen/interface/io/ring.h > @@ -208,12 +208,12 @@ struct __name##_back_ring { \ > > > #define RING_PUSH_REQUESTS(_r) do { \ > - wmb(); /* back sees requests /before/ updated producer index */ \ > + __smp_wmb(); /* back sees requests /before/ updated producer index */ \ > (_r)->sring->req_prod = (_r)->req_prod_pvt; \ > } while (0) > > #define RING_PUSH_RESPONSES(_r) do { \ > - wmb(); /* front sees responses /before/ updated producer index */ \ > + __smp_wmb(); /* front sees responses /before/ updated producer index */ \ > (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ > } while (0) > > @@ -250,9 +250,9 @@ struct __name##_back_ring { \ > #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ > RING_IDX __old = (_r)->sring->req_prod; \ > RING_IDX __new = (_r)->req_prod_pvt; \ > - wmb(); /* back sees requests /before/ updated producer index */ \ > + __smp_wmb(); /* back sees requests /before/ updated producer index */ \ > (_r)->sring->req_prod = __new; \ > - mb(); /* back sees new requests /before/ we check req_event */ \ > + __smp_mb(); /* back sees new requests /before/ we check req_event */ \ > (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ > (RING_IDX)(__new - __old)); \ > } while (0) > @@ -260,9 +260,9 @@ struct __name##_back_ring { \ > #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ > RING_IDX __old = (_r)->sring->rsp_prod; \ > RING_IDX __new = (_r)->rsp_prod_pvt; \ > - wmb(); /* front sees responses /before/ updated producer index */ \ > + __smp_wmb(); /* front sees responses /before/ updated producer index */ \ > (_r)->sring->rsp_prod = __new; \ > - mb(); /* front sees new responses /before/ we check rsp_event */ \ > + __smp_mb(); /* front sees new responses /before/ we check rsp_event */ \ > (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ > (RING_IDX)(__new - __old)); \ > } while (0) > @@ -271,7 +271,7 @@ struct __name##_back_ring { \ > (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ > if (_work_to_do) break; \ > (_r)->sring->req_event = (_r)->req_cons + 1; \ > - mb(); \ > + __smp_mb(); \ > (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ > } while (0) > > @@ -279,7 +279,7 @@ struct __name##_back_ring { \ > (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ > if (_work_to_do) break; \ > (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ > - mb(); \ > + __smp_mb(); \ > (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ > } while (0) > > -- > MST >