On Sat, Jul 28, 2012 at 2:11 PM, Will Deacon <will.deacon@xxxxxxx> wrote: > On Sat, Jul 28, 2012 at 11:08:31AM +0100, Russell King - ARM Linux wrote: >> On Fri, Jul 27, 2012 at 10:40:24PM +0100, Will Deacon wrote: >> > On Fri, Jul 27, 2012 at 10:06:37PM +0100, Russell King - ARM Linux wrote: >> > > We support booting a kernel on systems with or without SMP support, even >> > > with a SMP kernel. When the kernel is booted on such a system, it is >> > > undefined whether smp_cross_call() is a valid function pointer. >> > >> > So let's define it to point at a dummy function which explodes with a BUG if >> > the cpumask passed in isn't empty. That allows SMP kernels to do things like >> > `cross call to all other cores' without having to worry about whether there >> > are any other cores or not. >> >> We should not be even attempting to do any cross calls when there aren't >> any other CPUs in the system - that's rather the point of leaving it as >> a NULL pointer so it does explode on such systems. >> >> . the scheduler won't call smp_send_reschedule() when there are no other >> CPUs in the system. >> . timer ticks won't be broadcast to other CPUs if there are no other CPUs >> in the system. >> . function calls will not be issued to other CPUs if there are no other >> CPUs in the system. >> >> There is only one case where this doesn't happen, and that's the shutdown >> path. > > Ok, that's a pretty compelling argument you've got there :) > >> For instance, smp_call_function*() all check that the target CPUs are >> marked online before the arch code is requested to issue an IPI to the >> target CPU. > > Yes, thanks for making the case for the original patch. Consistency is the > most important thing with these APIs, so I'll go full circle and offer my > ack for the original patch: > > Acked-by: Will Deacon <will.deacon@xxxxxxx> > > The next question is: who's putting this into the patch system? > > Will Hi, I just put the patch with Will's Acked-by on the patch system. It was accepted as patch 7480/1 [1]. The patch is on top of today's linux-next (next-20120727). Thanks a lot and best regards, Javier [1] http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=7480/1 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
