Commit 60f3e00d authored May 08, 2017 by Davidlohr Bueso Committed by Linus Torvalds May 08, 2017

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 31a7c474 ("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>

parent f0cb8802

include/linux/ipc.h

+3 −4

Original line number	Diff line number	Diff line
		@@ -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;
		@@ -21,6 +20,6 @@ struct kern_ipc_perm
		umode_t mode;
		unsigned long seq;
		void *security;
		};
		} ____cacheline_aligned_in_smp;

		#endif /* _LINUX_IPC_H */

include/linux/sem.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -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 */