Messages in this thread Patch in this message | | | Date | Fri, 27 Feb 2015 20:15:30 +0000 | From | Will Deacon <> | Subject | Re: [RFC PATCH] arm64: cmpxchg.h: Bring ldxr and stxr closer |
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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.prani@gmail.com> > --- > arch/arm64/include/asm/cmpxchg.h | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-)
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> @@ -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.
Have a good weekend,
Will
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