From c1fb159db9f2e50e0f4025bed92a67a6a7bfa7b7 Mon Sep 17 00:00:00 2001 From: "Peter Zijlstra (Intel)" Date: Fri, 24 Apr 2015 14:56:32 -0400 Subject: locking/qspinlock: Add pending bit Because the qspinlock needs to touch a second cacheline (the per-cpu mcs_nodes[]); add a pending bit and allow a single in-word spinner before we punt to the second cacheline. It is possible so observe the pending bit without the locked bit when the last owner has just released but the pending owner has not yet taken ownership. In this case we would normally queue -- because the pending bit is already taken. However, in this case the pending bit is guaranteed to be released 'soon', therefore wait for it and avoid queueing. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Daniel J Blueman Cc: David Vrabel Cc: Douglas Hatch Cc: H. Peter Anvin Cc: Konrad Rzeszutek Wilk Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Paolo Bonzini Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Raghavendra K T Cc: Rik van Riel Cc: Scott J Norton Cc: Thomas Gleixner Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1429901803-29771-4-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar --- include/asm-generic/qspinlock_types.h | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) (limited to 'include') diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h index aec05c7ad2f6..7ee6632cb818 100644 --- a/include/asm-generic/qspinlock_types.h +++ b/include/asm-generic/qspinlock_types.h @@ -36,8 +36,9 @@ typedef struct qspinlock { * Bitfields in the atomic value: * * 0- 7: locked byte - * 8- 9: tail index - * 10-31: tail cpu (+1) + * 8: pending + * 9-10: tail index + * 11-31: tail cpu (+1) */ #define _Q_SET_MASK(type) (((1U << _Q_ ## type ## _BITS) - 1)\ << _Q_ ## type ## _OFFSET) @@ -45,7 +46,11 @@ typedef struct qspinlock { #define _Q_LOCKED_BITS 8 #define _Q_LOCKED_MASK _Q_SET_MASK(LOCKED) -#define _Q_TAIL_IDX_OFFSET (_Q_LOCKED_OFFSET + _Q_LOCKED_BITS) +#define _Q_PENDING_OFFSET (_Q_LOCKED_OFFSET + _Q_LOCKED_BITS) +#define _Q_PENDING_BITS 1 +#define _Q_PENDING_MASK _Q_SET_MASK(PENDING) + +#define _Q_TAIL_IDX_OFFSET (_Q_PENDING_OFFSET + _Q_PENDING_BITS) #define _Q_TAIL_IDX_BITS 2 #define _Q_TAIL_IDX_MASK _Q_SET_MASK(TAIL_IDX) @@ -54,5 +59,6 @@ typedef struct qspinlock { #define _Q_TAIL_CPU_MASK _Q_SET_MASK(TAIL_CPU) #define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET) +#define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET) #endif /* __ASM_GENERIC_QSPINLOCK_TYPES_H */ -- cgit v1.2.3