On Fri, Feb 27, 2015 at 3:15 PM, Will Deacon <will.dea...@arm.com> wrote: > On Fri, Feb 27, 2015 at 08:09:17PM +0000, Pranith Kumar wrote: >> ARM64 documentation recommends keeping exclusive loads and stores as close as >> possible. Any instructions which do not depend on the value loaded should be >> moved outside. >> >> In the current implementation of cmpxchg(), there is a mov instruction which >> can >> be pulled before the load exclusive instruction without any change in >> functionality. This patch does that change. >> >> Signed-off-by: Pranith Kumar <bobby.pr...@gmail.com> >> --- >> arch/arm64/include/asm/cmpxchg.h | 10 +++++----- >> 1 file changed, 5 insertions(+), 5 deletions(-) > > [...] > >> @@ -166,11 +166,11 @@ static inline int __cmpxchg_double(volatile void >> *ptr1, volatile void *ptr2, >> VM_BUG_ON((unsigned long *)ptr2 - (unsigned long *)ptr1 != 1); >> do { >> asm volatile("// __cmpxchg_double8\n" >> + " mov %w0, #0\n" >> " ldxp %0, %1, %2\n" > > Seriously, you might want to test this before you mindlessly make changes to > low-level synchronisation code. Not only is the change completely unnecessary > but it is actively harmful. >
Oops, I apologize for this. I should have looked more closely. It is wrong to do this in cmpxchg_double(). What about the other cases? -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/