On Wed, 08 Aug 2007 17:08:44 -0400 Chris Snook <[EMAIL PROTECTED]> wrote:
> 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? I'm not Andi, but this not-Andi thinks that permitting the compiler to cache the results of atomic_read() is dumb. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
