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SubjectRe: [PATCH] i386: Fix a couple busy loops in mach_wakecpu.h:wait_for_init_deassert()
Denys Vlasenko wrote:
> On Friday 24 August 2007 18:06, Christoph Lameter wrote:
>> On Fri, 24 Aug 2007, Satyam Sharma wrote:
>>> But if people do seem to have a mixed / confused notion of atomicity
>>> and barriers, and if there's consensus, then as I'd said earlier, I
>>> have no issues in going with the consensus (eg. having API variants).
>>> Linus would be more difficult to convince, however, I suspect :-)
>> The confusion may be the result of us having barrier semantics in
>> atomic_read. If we take that out then we may avoid future confusions.
>
> I think better name may help. Nuke atomic_read() altogether.
>
> n = atomic_value(x); // doesnt hint as strongly at reading as "atomic_read"
> n = atomic_fetch(x); // yes, we _do_ touch RAM
> n = atomic_read_uncached(x); // or this
>
> How does that sound?

atomic_value() vs. atomic_fetch() should be rather unambiguous.
atomic_read_uncached() begs the question of precisely which cache we are
avoiding, and could itself cause confusion.

So, if I were writing atomic.h from scratch, knowing what I know now, I think
I'd use atomic_value() and atomic_fetch(). The problem is that there are a lot
of existing users of atomic_read(), and we can't write a script to correctly
guess their intent. I'm not sure auditing all uses of atomic_read() is really
worth the comparatively miniscule benefits.

We could play it safe and convert them all to atomic_fetch(), or we could
acknowledge that changing the semantics 8 months ago was not at all disastrous,
and make them all atomic_value(), allowing people to use atomic_fetch() where
they really care.

-- Chris
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