David Howells writes: > On NUMA PowerPC, should mmiowb() be a SYNC or an EIEIO instruction then? Those > do inter-component synchronisation. We actually have quite heavy synchronization in read*/write* on PPC, and mmiowb can safely be a no-op. It would be nice to be able to have lighter-weight synchronization, but I'm sure we would see lots of subtle driver bugs cropping up if we did. write* do a full memory barrier (sync) after the store, and read* explicitly wait for the data to come back before. If you ask me, the need for mmiowb on some platforms merely shows that those platforms' implementations of spinlocks and read*/write* are buggy... Paul. - 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/
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