On Thu, Feb 19, 2009 at 05:47:20PM +1100, Benjamin Herrenschmidt wrote: > > > It might hide some architecture-specific implementation issue, of course, > > so random amounts of "smp_mb()"s sprinkled around might well make some > > architecture "work", but it's in no way guaranteed. A smp_mb() does not > > guarantee that some separate IPI network is ordered - that may well take > > some random machine-specific IO cycle. > > > > That said, at least on x86, taking an interrupt should be a serializing > > event, so there should be no reason for anything on the receiving side. > > The _sending_ side might need to make sure that there is serialization > > when generating the IPI (so that the IPI cannot happen while the writes > > are still in some per-CPU write buffer and haven't become part of the > > cache coherency domain). > > > > And at least on x86 it's actually pretty hard to generate out-of-order > > accesses to begin with (_regardless_ of any issues external to the CPU). > > You have to work at it, and use a WC memory area, and I'm pretty sure we > > use UC for the apic accesses. > > On powerpc, I suspect an smp_mb() on the sender would be useful... it > mostly depends how the IPI is generated but in most case it's going to > be an MMIO write, ie non-cached write which isn't ordered vs. any > previous cached store except using a full sync (which is what smp_mb() > does). So your arch_send_call_function_single_ipi etc need to ensure this, right? Generic code obviously has no idea about how to do it. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
