Heiko Carstens wrote:
On Wed, Aug 08, 2007 at 03:21:31AM -0700, David Miller wrote:
From: Heiko Carstens <[email protected]>
Date: Wed, 8 Aug 2007 11:33:00 +0200
Just saw this while grepping for atomic_reads in a while loops.
Maybe we should re-add the volatile to atomic_t. Not sure.
I think whatever the choice, it should be done consistently
on every architecture.
It's just asking for trouble if your arch does it differently from
every other.
Well..currently it's i386/x86_64 and s390 which have no volatile
in atomic_t. And yes, of course I agree it should be consistent
across all architectures. But it isn't.
Based on recent discussion, it's pretty clear that there's a lot of
confusion about this. A lot of people (myself included, until I thought
about it long and hard) will reasonably assume that calling
atomic_read() will actually read the value from memory. Leaving out the
volatile declaration seems like a pessimization to me. If you force
people to use barrier() everywhere they're working with atomic_t, it
will force re-reads of all the non-atomic data in use as well, which
will cause more memory fetches of things that generally don't need
barrier(). That and it's a bug waiting to happen.
Andi -- your thoughts on the matter?
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