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Avoid false sharing for snapshot by aligning properly the

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data of the triple buffer to a cache boundary.
This commit is contained in:
Patrick Pelissier committed 2018-02-10 08:29:34 +01:00
1 parent c71de15cb0
commit 67856a98af
1 file changed
+18 -12
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m-snapshot.h
+18 -12
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@@ -99,8 +99,14 @@
#define SNAPSHOTI_DEF2(name, type, oplist) \
\
/* Create an aligned type to avoid false sharing between threads */ \
typedef struct M_C(name, _aligned_type_s) { \
type x; \
char align[M_ALIGN_FOR_CACHELINE_EXCLUSION > sizeof(type) ? M_ALIGN_FOR_CACHELINE_EXCLUSION - - sizeof(type) : 1]; \
} M_C(name, _aligned_type_t); \
\
typedef struct M_C(name, _s) { \
type data[SNAPSHOTI_MAX_BUFFER]; \
M_C(name, _aligned_type_t) data[SNAPSHOTI_MAX_BUFFER]; \
atomic_uchar flags; \
} M_C(name, _t)[1]; \
\
@@ -110,7 +116,7 @@
{ \
assert(snap != NULL); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_INIT oplist(snap->data[i]); \
M_GET_INIT oplist(snap->data[i].x); \
} \
atomic_init (&snap->flags, SNAPSHOTI_FLAG(0, 1, 2, 0)); \
SNAPSHOTI_CONTRACT(snap); \
@@ -120,17 +126,17 @@
{ \
SNAPSHOTI_CONTRACT(snap); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_CLEAR oplist(snap->data[i]); \
M_GET_CLEAR oplist(snap->data[i].x); \
} \
} \
\
\
static inline void M_C(name, _init_set)(M_C(name, _t) snap, \
M_C(name, _t) org) \
{ \
SNAPSHOTI_CONTRACT(org); \
assert(snap != NULL && snap != org); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_INIT_SET oplist(snap->data[i], org->data[i]); \
M_GET_INIT_SET oplist(snap->data[i].x, org->data[i].x); \
} \
atomic_init (&snap->flags, atomic_load(&org->flags)); \
SNAPSHOTI_CONTRACT(snap); \
@@ -142,7 +148,7 @@
SNAPSHOTI_CONTRACT(snap); \
SNAPSHOTI_CONTRACT(org); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_SET oplist(snap->data[i], org->data[i]); \
M_GET_SET oplist(snap->data[i].x, org->data[i].x); \
} \
atomic_init (&snap->flags, atomic_load(&org->flags)); \
SNAPSHOTI_CONTRACT(snap); \
@@ -155,7 +161,7 @@
SNAPSHOTI_CONTRACT(org); \
assert(snap != NULL && snap != org); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_INIT_MOVE oplist(snap->data[i], org->data[i]); \
M_GET_INIT_MOVE oplist(snap->data[i].x, org->data[i].x); \
} \
atomic_store (&snap->flags, atomic_load(&org->flags)); \
atomic_store (&org->flags, SNAPSHOTI_FLAG(0,0,0,0) ); \
@@ -171,7 +177,7 @@
SNAPSHOTI_CONTRACT(org); \
assert(snap != org); \
for(int i = 0; i < SNAPSHOTI_MAX_BUFFER; i++) { \
M_GET_MOVE oplist(snap->data[i], org->data[i]); \
M_GET_MOVE oplist(snap->data[i].x, org->data[i].x); \
} \
atomic_store (&snap->flags, atomic_load(&org->flags)); \
atomic_store (&org->flags, SNAPSHOTI_FLAG(0,0,0,0) ); \
@@ -194,7 +200,7 @@
} while (!atomic_compare_exchange_weak (&snap->flags, &origFlags, \
nextFlags)); \
/* Return new write buffer for new updating */ \
return &snap->data[SNAPSHOTI_W(nextFlags)]; \
return &snap->data[SNAPSHOTI_W(nextFlags)].x; \
} \
\
static inline const type *M_C(name, _read)(M_C(name, _t) snap) \
@@ -216,7 +222,7 @@
} while (!atomic_compare_exchange_weak (&snap->flags, &origFlags, \
nextFlags)); \
/* Return current read buffer */ \
return M_CONST_CAST(type, &snap->data[SNAPSHOTI_R(nextFlags)]); \
return M_CONST_CAST(type, &snap->data[SNAPSHOTI_R(nextFlags)].x); \
} \
\
static inline bool M_C(name, _updated_p)(M_C(name, _t) snap) \
@@ -230,14 +236,14 @@
{ \
SNAPSHOTI_CONTRACT(snap); \
unsigned char flags = atomic_load(&snap->flags); \
return &snap->data[SNAPSHOTI_W(flags)]; \
return &snap->data[SNAPSHOTI_W(flags)].x; \
} \
\
static inline const type *M_C(name, _get_read_buffer)(M_C(name, _t) snap) \
{ \
SNAPSHOTI_CONTRACT(snap); \
unsigned char flags = atomic_load(&snap->flags); \
return M_CONST_CAST(type, &snap->data[SNAPSHOTI_R(flags)]); \
return M_CONST_CAST(type, &snap->data[SNAPSHOTI_R(flags)].x); \
} \
// FIXME: Method SWAP ?