futexes: allow architectures to skip futex_atomic_cmpxchg_inatomic() test
PATCH 1/1 futexes: allow architectures to skip futex_atomic_cmpxchg_inatomic() test
If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there is no runtime check necessary, allow to skip the test within futex_init().
This allows to get rid of some code which would always give the same result, and also allows the compiler to optimize a couple of if statements away.
Cc Geert Uytterhoeven <[email protected]>
Cc Finn Thain <[email protected]>
Signed-off-by Heiko Carstens <[email protected]>
--- arch/s390/Kconfig | 1 + include/linux/futex.h | 4 ++++ init/Kconfig | 7 +++++++ kernel/futex.c | 37 ++++++++++++++++++++++++------------- 4 files changed, 36 insertions(+), 13 deletions(-)
arch/s390/Kconfig +1 -0
@@ -117,6 +117,7 @@ config S390 select HAVE_FUNCTION_GRAPH_TRACER select HAVE_FUNCTION_TRACER select HAVE_FUNCTION_TRACE_MCOUNT_TEST + select HAVE_FUTEX_CMPXCHG if FUTEX select HAVE_KERNEL_BZIP2 select HAVE_KERNEL_GZIP select HAVE_KERNEL_LZ4
include/linux/futex.h +4 -0
@@ -55,7 +55,11 @@ union futex_key {#ifdef CONFIG_FUTEX extern void exit_robust_list (struct task_struct *curr);extern void exit_pi_state_list (struct task_struct *curr); +#ifdef CONFIG_HAVE_FUTEX_CMPXCHG +#define futex_cmpxchg_enabled 1 +#else extern int futex_cmpxchg_enabled; +#endif #else static inline void exit_robust_list (struct task_struct *curr) {
init/Kconfig +7 -0
@@ -1387,6 +1387,13 @@ config FUTEX support for "fast userspace mutexes". The resulting kernel may not run glibc-based applications correctly. +config HAVE_FUTEX_CMPXCHG + bool + help + Architectures should select this if futex_atomic_cmpxchg_inatomic() + is implemented and always working. This removes a couple of runtime + checks. + config EPOLL bool "Enable eventpoll support" if EXPERT default y
kernel/futex.c +24 -13
@@ -157,7 +157,9 @@* enqueue. */ +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG int __read_mostly futex_cmpxchg_enabled; +#endif /* * Futex flags used to encode options to functions and preserve them across
@@ -2843,9 +2845,28 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,return do_futex (uaddr, op, val, tp, uaddr2, val2, val3); } -static int __init futex_init (void ) +static void __init futex_detect_cmpxchg (void ) { +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG u32 curval; + +/* +* This will fail and we want it. Some arch implementations do +* runtime detection of the futex_atomic_cmpxchg_inatomic() +* functionality. We want to know that before we call in any +* of the complex code paths. Also we want to prevent +* registration of robust lists in that case. NULL is +* guaranteed to fault and we get -EFAULT on functional +* implementation, the non-functional ones will return +* -ENOSYS. +*/ +if (cmpxchg_futex_value_locked (&curval,NULL ,0 ,0 ) == -EFAULT ) + futex_cmpxchg_enabled =1 ; +#endif +} + +static int __init futex_init (void ) +{unsigned int futex_shift;unsigned long i;
@@ -2861,18 +2882,8 @@ static int __init futex_init(void) &futex_shift,NULL , futex_hashsize, futex_hashsize); futex_hashsize =1UL << futex_shift; -/* -* This will fail and we want it. Some arch implementations do -* runtime detection of the futex_atomic_cmpxchg_inatomic() -* functionality. We want to know that before we call in any -* of the complex code paths. Also we want to prevent -* registration of robust lists in that case. NULL is -* guaranteed to fault and we get -EFAULT on functional -* implementation, the non-functional ones will return -* -ENOSYS. -*/ -if (cmpxchg_futex_value_locked (&curval,NULL ,0 ,0 ) == -EFAULT ) - futex_cmpxchg_enabled =1 ; + +futex_detect_cmpxchg ();for (i =0 ; i < futex_hashsize; i++) {plist_head_init (&futex_queues[i].chain);
Signature · 1 line
1.8.4.5
tip-bot for Heiko Carstens
merge bot[tip:core/locking] futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
Commit-ID: 03b8c7b623c80af264c4c8d6111e5c6289933666 Gitweb: http://git.kernel.org/tip/03b8c7b623c80af264c4c8d6111e5c6289933666 Author: Heiko Carstens <[email protected]> AuthorDate: Sun, 2 Mar 2014 13:09:47 +0100 Committer: Thomas Gleixner <[email protected]> CommitDate: Mon, 3 Mar 2014 11:32:08 +0100
futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there is no runtime check necessary, allow to skip the test within futex_init().
This allows to get rid of some code which would always give the same result, and also allows the compiler to optimize a couple of if statements away.
Signed-off-by Heiko Carstens <[email protected]>
Cc Finn Thain <[email protected]>
Cc Geert Uytterhoeven <[email protected]>
Signed-off-by Thomas Gleixner <[email protected]>
--- arch/s390/Kconfig | 1 + include/linux/futex.h | 4 ++++ init/Kconfig | 7 +++++++ kernel/futex.c | 37 ++++++++++++++++++++++++------------- 4 files changed, 36 insertions(+), 13 deletions(-)
arch/s390/Kconfig +1 -0
@@ -117,6 +117,7 @@ config S390 select HAVE_FUNCTION_GRAPH_TRACER select HAVE_FUNCTION_TRACER select HAVE_FUNCTION_TRACE_MCOUNT_TEST + select HAVE_FUTEX_CMPXCHG if FUTEX select HAVE_KERNEL_BZIP2 select HAVE_KERNEL_GZIP select HAVE_KERNEL_LZ4
include/linux/futex.h +4 -0
@@ -55,7 +55,11 @@ union futex_key {#ifdef CONFIG_FUTEX extern void exit_robust_list (struct task_struct *curr);extern void exit_pi_state_list (struct task_struct *curr); +#ifdef CONFIG_HAVE_FUTEX_CMPXCHG +#define futex_cmpxchg_enabled 1 +#else extern int futex_cmpxchg_enabled; +#endif #else static inline void exit_robust_list (struct task_struct *curr) {
init/Kconfig +7 -0
@@ -1387,6 +1387,13 @@ config FUTEX support for "fast userspace mutexes". The resulting kernel may not run glibc-based applications correctly. +config HAVE_FUTEX_CMPXCHG + bool + help + Architectures should select this if futex_atomic_cmpxchg_inatomic() + is implemented and always working. This removes a couple of runtime + checks. + config EPOLL bool "Enable eventpoll support" if EXPERT default y
kernel/futex.c +24 -13
@@ -157,7 +157,9 @@* enqueue. */ +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG int __read_mostly futex_cmpxchg_enabled; +#endif /* * Futex flags used to encode options to functions and preserve them across
@@ -2843,9 +2845,28 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,return do_futex (uaddr, op, val, tp, uaddr2, val2, val3); } -static int __init futex_init (void ) +static void __init futex_detect_cmpxchg (void ) { +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG u32 curval; + +/* +* This will fail and we want it. Some arch implementations do +* runtime detection of the futex_atomic_cmpxchg_inatomic() +* functionality. We want to know that before we call in any +* of the complex code paths. Also we want to prevent +* registration of robust lists in that case. NULL is +* guaranteed to fault and we get -EFAULT on functional +* implementation, the non-functional ones will return +* -ENOSYS. +*/ +if (cmpxchg_futex_value_locked (&curval,NULL ,0 ,0 ) == -EFAULT ) + futex_cmpxchg_enabled =1 ; +#endif +} + +static int __init futex_init (void ) +{unsigned int futex_shift;unsigned long i;
@@ -2861,18 +2882,8 @@ static int __init futex_init(void) &futex_shift,NULL , futex_hashsize, futex_hashsize); futex_hashsize =1UL << futex_shift; -/* -* This will fail and we want it. Some arch implementations do -* runtime detection of the futex_atomic_cmpxchg_inatomic() -* functionality. We want to know that before we call in any -* of the complex code paths. Also we want to prevent -* registration of robust lists in that case. NULL is -* guaranteed to fault and we get -EFAULT on functional -* implementation, the non-functional ones will return -* -ENOSYS. -*/ -if (cmpxchg_futex_value_locked (&curval,NULL ,0 ,0 ) == -EFAULT ) - futex_cmpxchg_enabled =1 ; + +futex_detect_cmpxchg ();for (i =0 ; i < futex_hashsize; i++) {plist_head_init (&futex_queues[i].chain);