From mboxrd@z Thu Jan 1 00:00:00 1970 From: sboyd@codeaurora.org (Stephen Boyd) Date: Thu, 25 Jul 2013 10:37:48 -0700 Subject: [PATCH 4/6] ARM: locks: prefetch the destination word for write prior to strex In-Reply-To: <51F160EA.6030800@codeaurora.org> References: <1374579389-32704-1-git-send-email-will.deacon@arm.com> <1374579389-32704-5-git-send-email-will.deacon@arm.com> <20130724111841.GD11072@mudshark.cambridge.arm.com> <51F160EA.6030800@codeaurora.org> Message-ID: <51F1626C.3050008@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/25/13 10:31, Stephen Boyd wrote: > On 07/24/13 04:18, Will Deacon wrote: >> On Tue, Jul 23, 2013 at 09:10:33PM +0100, Nicolas Pitre wrote: >>> On Tue, 23 Jul 2013, Will Deacon wrote: >>> >>>> The cost of changing a cacheline from shared to exclusive state can be >>>> significant, especially when this is triggered by an exclusive store, >>>> since it may result in having to retry the transaction. >>>> >>>> This patch prefixes our {spin,read,write}_[try]lock implementations with >>>> pldw instructions (on CPUs which support them) to try and grab the line >>>> in exclusive state from the start. >>>> >>>> Signed-off-by: Will Deacon >>>> --- >>>> arch/arm/include/asm/spinlock.h | 9 ++++++++- >>>> 1 file changed, 8 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h >>>> index 0de7bec..3e1cc9d 100644 >>>> --- a/arch/arm/include/asm/spinlock.h >>>> +++ b/arch/arm/include/asm/spinlock.h >>>> @@ -5,7 +5,7 @@ >>>> #error SMP not supported on pre-ARMv6 CPUs >>>> #endif >>>> >>>> -#include >>>> +#include >>>> >>>> /* >>>> * sev and wfe are ARMv6K extensions. Uniprocessor ARMv6 may not have the K >>>> @@ -70,6 +70,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) >>>> u32 newval; >>>> arch_spinlock_t lockval; >>>> >>>> + prefetchw((const void *)&lock->slock); >>> Couldn't that cast be carried in the definition of prefetchw() instead? >> I think that would mean implementing prefetchw as a macro rather than an >> inline function, since the core code expects to pass a const pointer and GCC >> gets angry if the type signatures don't match. > Maybe I'm wrong, but can't you just remove the casts and leave the > function as static inline? const void * is pretty much telling the > compiler to turn off type checking. > Oh joy. Why is rwlock's lock member marked volatile? -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation