On Mon, Jul 07, 2014 at 11:50:19AM -0700, Jason Low wrote:
> Recent optimistic spinning additions to rwsem provide significant performance
> benefits on many workloads on large machines. The cost of it was increasing
> the size of the rwsem structure by up to 128 bits.
>
> However, now that the previous patches in this series bring the overhead of
> struct optimistic_spin_queue to 32 bits, this patch reorders some fields in
> struct rw_semaphore such that we can reduce the overhead of the rwsem
> structure
> by 64 bits (on 64 bit systems).
>
> The extra overhead required for rwsem optimistic spinning would now be up
> to 8 additional bytes instead of up to 16 bytes. Additionally, the size of
> rwsem would now be more in line with mutexes.
>
> Signed-off-by: Jason Low <[email protected]>
> ---
> include/linux/rwsem.h | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 9fdcdd0..f6c54c0 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -24,15 +24,15 @@ struct rw_semaphore;
> /* All arch specific implementations share the same struct */
> struct rw_semaphore {
> long count;
> - raw_spinlock_t wait_lock;
> struct list_head wait_list;
> + raw_spinlock_t wait_lock;
> #ifdef CONFIG_SMP
> + struct optimistic_spin_queue osq; /* spinner MCS lock */
> /*
> * Write owner. Used as a speculative check to see
> * if the owner is running on the cpu.
> */
> struct task_struct *owner;
> - struct optimistic_spin_queue osq; /* spinner MCS lock */
> #endif
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> struct lockdep_map dep_map;
> @@ -66,10 +66,10 @@ static inline int rwsem_is_locked(struct rw_semaphore
> *sem)
> #if defined(CONFIG_SMP) && !defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
> #define __RWSEM_INITIALIZER(name) \
> { RWSEM_UNLOCKED_VALUE, \
> - __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
> LIST_HEAD_INIT((name).wait_list), \
> + __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
> + { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }, /* osq */ \
> NULL, /* owner */ \
> - { ATOMIC_INIT(OSQ_UNLOCKED_VAL) } /* osq */ \
> __RWSEM_DEP_MAP_INIT(name) }
> #else
> #define __RWSEM_INITIALIZER(name) \
This gets me:
../init/init_task.c:14:44: error: expected expression before ‘,’ token
{ ATOMIC_INIT(OSQ_UNLOCKED_VAL) }, /* osq */ \
- NULL, /* owner */ \
+ NULL /* owner */ \
__RWSEM_DEP_MAP_INIT(name) }
Makes it work again.
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