From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: sysv,ipc: cacheline align kern_ipc_perm
Assign 'struct kern_ipc_perm' its own cacheline to avoid false sharing
with sysv ipc calls. While the structure itself is rather read-mostly
throughout the lifespan of ipc, the spinlock causes most of the
invalidations. One example is 31a7c4746e9 ("ipc/sem.c: cacheline align
the ipc spinlock for semaphores"). Therefore, extend this to all ipc.
The effect of cacheline alignment on sems can be seen in sembench, which
deals mostly with semtimedop wait/wakes is seen to improve raw throughput
(worker loops) between 8 to 12% on a 24-core x86 with over 4 threads.
Link: http://lkml.kernel.org/r/1486673582-6979-4-git-send-email-dave@xxxxxxxxxxxx
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/ipc.h | 7 +++----
include/linux/sem.h | 3 +--
2 files changed, 4 insertions(+), 6 deletions(-)
diff -puN include/linux/ipc.h~sysvipc-cacheline-align-kern_ipc_perm include/linux/ipc.h
--- a/include/linux/ipc.h~sysvipc-cacheline-align-kern_ipc_perm
+++ a/include/linux/ipc.h
@@ -8,8 +8,7 @@
#define IPCMNI 32768 /* <= MAX_INT limit for ipc arrays (including sysctl changes) */
/* used by in-kernel data structures */
-struct kern_ipc_perm
-{
+struct kern_ipc_perm {
spinlock_t lock;
bool deleted;
int id;
@@ -18,9 +17,9 @@ struct kern_ipc_perm
kgid_t gid;
kuid_t cuid;
kgid_t cgid;
- umode_t mode;
+ umode_t mode;
unsigned long seq;
void *security;
-};
+} ____cacheline_aligned_in_smp;
#endif /* _LINUX_IPC_H */
diff -puN include/linux/sem.h~sysvipc-cacheline-align-kern_ipc_perm include/linux/sem.h
--- a/include/linux/sem.h~sysvipc-cacheline-align-kern_ipc_perm
+++ a/include/linux/sem.h
@@ -10,8 +10,7 @@ struct task_struct;
/* One sem_array data structure for each set of semaphores in the system. */
struct sem_array {
- struct kern_ipc_perm ____cacheline_aligned_in_smp
- sem_perm; /* permissions .. see ipc.h */
+ struct kern_ipc_perm sem_perm; /* permissions .. see ipc.h */
time_t sem_ctime; /* last change time */
struct sem *sem_base; /* ptr to first semaphore in array */
struct list_head pending_alter; /* pending operations */
_
--
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