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
commit 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@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 9d84942..71fd92d 100644 (file)
--- a/include/linux/ipc.h
+++ b/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 --git a/include/linux/sem.h b/include/linux/sem.h
index 4fc222f..9edec92 100644 (file)
--- a/include/linux/sem.h
+++ b/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 */