On Thu, 14 Oct 2010 19:40:25 +0200 Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> wrote: > 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 We could just omit the HAVE_MUTEX_CPU_RELAX > --- 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 and do `#ifndef mutex_cpu_relax' here. That's a pretty common trick. It's best to add a comment telling people which arch header file should define mutex_cpu_relax, so everyone does it the same way. It should perhaps be called arch_mutex_cpu_relax(). -- 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
