From: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> The spinning mutex implementation uses cpu_relax() in busy loops as a compiler barrier. Depending on the architecture, cpu_relax() may do more than needed in this specific mutex spin loops. On System z we also give up the time slice of the virtual cpu in cpu_relax(), which prevents effective spinning on the mutex. This patch replaces cpu_relax() in the spinning mutex code with a new function mutex_cpu_relax(), which can be defined by each architecture that selects HAVE_MUTEX_CPU_RELAX. The default is still cpu_relax(), so this patch should not affect other architectures than System z for now. Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> --- arch/Kconfig | 3 +++ arch/s390/Kconfig | 1 + arch/s390/include/asm/mutex.h | 2 ++ include/linux/mutex.h | 4 ++++ kernel/mutex.c | 2 +- kernel/sched.c | 2 +- 6 files changed, 12 insertions(+), 2 deletions(-) --- a/arch/Kconfig +++ b/arch/Kconfig @@ -158,4 +158,7 @@ config HAVE_PERF_EVENTS_NMI subsystem. Also has support for calculating CPU cycle events to determine how many clock cycles in a given period. +config HAVE_MUTEX_CPU_RELAX + bool + source "kernel/gcov/Kconfig" --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -100,6 +100,7 @@ config S390 select HAVE_KERNEL_BZIP2 select HAVE_KERNEL_LZMA select HAVE_KERNEL_LZO + select HAVE_MUTEX_CPU_RELAX select ARCH_INLINE_SPIN_TRYLOCK select ARCH_INLINE_SPIN_TRYLOCK_BH select ARCH_INLINE_SPIN_LOCK --- a/arch/s390/include/asm/mutex.h +++ b/arch/s390/include/asm/mutex.h @@ -7,3 +7,5 @@ */ #include <asm-generic/mutex-dec.h> + +#define mutex_cpu_relax() barrier() --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -160,4 +160,8 @@ extern int mutex_trylock(struct mutex *l extern void mutex_unlock(struct mutex *lock); extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock); +#ifndef CONFIG_HAVE_MUTEX_CPU_RELAX +#define mutex_cpu_relax() cpu_relax() +#endif + #endif --- a/kernel/mutex.c +++ b/kernel/mutex.c @@ -199,7 +199,7 @@ __mutex_lock_common(struct mutex *lock, * memory barriers as we'll eventually observe the right * values at the cost of a few extra spins. */ - cpu_relax(); + mutex_cpu_relax(); } #endif spin_lock_mutex(&lock->wait_lock, flags); --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3888,7 +3888,7 @@ int mutex_spin_on_owner(struct mutex *lo if (task_thread_info(rq->curr) != owner || need_resched()) return 0; - cpu_relax(); + mutex_cpu_relax(); } return 1; -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
