Re: [Qemu-devel] [RFC 1/6] bitmap: add atomic set functions

[Stefan Hajnoczi]

On Thu, Nov 27, 2014 at 05:42:41PM +0100, Paolo Bonzini wrote:
> 
> 
> On 27/11/2014 13:29, Stefan Hajnoczi wrote:
> > +void bitmap_set_atomic(unsigned long *map, long start, long nr)
> > +{
> > +    unsigned long *p = map + BIT_WORD(start);
> > +    const long size = start + nr;
> > +    int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
> > +    unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start);
> > +
> > +    while (nr - bits_to_set >= 0) {
> > +        atomic_or(p, mask_to_set);
> 
> atomic_or is unnecessary while mask_to_set is ~0UL.  I think not even a
> smp_wmb() is necessary.

Okay, I can split this into the ~0UL case and the atomic case.

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