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.
Have a good weekend,
Will
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