Re: [Xen-devel] [PATCH v2 34/34] xen/io: use virt_xxx barriers

[David Vrabel]

On 31/12/15 19:10, 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 virt_xxx barriers which serve this exact purpose.

Acked-by: David Vrabel 

David
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Re: [PATCH v2 34/34] xen/io: use virt_xxx barriers

[Stefano Stabellini]

On Thu, 31 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 virt_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..21f4fbd 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 */  \
> +virt_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 */
> \
> +virt_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 */  \
> +virt_wmb(); /* back sees requests /before/ updated producer index */ 
> \
>  (_r)->sring->req_prod = __new;   \
> -mb(); /* back sees new requests /before/ we check req_event */   \
> +virt_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 */
> \
> +virt_wmb(); /* front sees responses /before/ updated producer index */   
> \
>  (_r)->sring->rsp_prod = __new;   \
> -mb(); /* front sees new responses /before/ we check rsp_event */ \
> +virt_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();\
> +virt_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();\
> +virt_mb();   
> \
>  (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);   
> \
>  } while (0)
>  
> -- 
> MST
> 
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[PATCH v2 34/34] xen/io: use virt_xxx barriers

[Michael S. Tsirkin]

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 virt_xxx barriers which serve this exact purpose.

Signed-off-by: Michael S. Tsirkin 
---
 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..21f4fbd 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 */\
+virt_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 */  \
+virt_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 */\
+virt_wmb(); /* back sees requests /before/ updated producer index */   
\
 (_r)->sring->req_prod = __new; \
-mb(); /* back sees new requests /before/ we check req_event */ \
+virt_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 */  \
+virt_wmb(); /* front sees responses /before/ updated producer index */ 
\
 (_r)->sring->rsp_prod = __new; \
-mb(); /* front sees new responses /before/ we check rsp_event */   \
+virt_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();  \
+virt_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();  \
+virt_mb(); \
 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
 } while (0)
 
-- 
MST

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