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SubjectRe: [PATCH v4 1/3] qspinlock: Introducing a 4-byte queue spinlock implementation
On Tue, Feb 18, 2014 at 02:39:31PM -0500, Waiman Long wrote:
> The #ifdef is harder to take away here. The point is that doing a 32-bit
> exchange may accidentally steal the lock with the additional code to handle
> that. Doing a 16-bit exchange, on the other hand, will never steal the lock
> and so don't need the extra handling code. I could construct a function with
> different return values to handle the different cases if you think it will
> make the code easier to read.

Does it really pay to use xchg() with all those fixup cases? Why not
have a single cmpxchg() loop that does just the exact atomic op you
want?


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