RE: [Xen-devel] RFC: 32 bits as smallest atomic size.

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> Right now there is a single problematic cmpxchg user, 
> grant_entry_t, and the impact of the fix is tiny (make the 
> 'flags' member 4 bytes). Is that too large an inconvenience?

That would make grant table entries 12 bytes rather than 8 bytes, which
is not ideal given that you can end up needing quite a lot of them,
particularly when the cacheline packing is considered. 

Perhaps the best thing to do would be to change that particular instance
of cmpxchg into cmpxchg_16, where we handle the subword case on
architectures which can't do it directly by rounding down the address,
doing a read, insert, and cmpxchg. 

This seems a better fix, at least to me.

Ian

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