[Xen-devel] [PATCH 32/34] xen/io: use __smp_XXX barriers

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

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 <mst@xxxxxxxxxx>
---
 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


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