Re: [Xen-devel] [PATCH v3 1/2] x86: simplify nonâatomic bitops

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/03/15 14:53, Jan Beulich wrote:
> - being non-atomic, their pointer arguments shouldn't be volatile-
>    qualified
> - their (half fake) memory operands can be a single "+m" instead of
>    being both an output and an input
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
After further consideration, would it not be better to change the 
non-atomic variants to being straight C.
e.g.

static inline void __set_bit(int nr, void *_addr)
{
    int *addr = _addr;
    addr[nr / sizeof(int)] |= (1U << (nr % sizeof(int)));
}

This would drop the memory clobber from the asm statement and allow the 
compiler to optimise repeated __set_bit() calls to the same word into a 
single action.
~Andrew

(On a separate note, I feel that all of these operations should be 
acting on unsigned rather than signed ints, but that applies to all of 
these operations, not just the non-atomic ones)
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