On Wed, Oct 06, 2010 at 07:44:14AM -0700, Tony Lindgren wrote: > * Russell King - ARM Linux <li...@arm.linux.org.uk> [101005 15:24]: > > On Tue, Oct 05, 2010 at 03:19:52PM -0700, Tony Lindgren wrote: > > > * Tony Lindgren <t...@atomide.com> [100907 20:04]: > > > > This should not be needed when running on UP systems. > > > > > > > > Additionally we will also get an undefined instruction on ARM cores > > > > without the extended CPUID registers with CONFIG_SMP_ON_UP. > > > > > > > > Also, we can now remove the is_smp() test from mmu.c. > > > > > > Just FYI, I've updated this one more time with to use cpus_empty > > > instead of !smp_on_up() here as well. > > > > What's the rationale? > > With CPU hotplug if the other SMP cores are unplugged for PM or > other reasons, no need to do the broadcast.
Yes, but why this expensive test when the smp_on_up() is much cheaper? smp_call_function_many() already takes care of the "no other CPUs" case, which is used by on_each_cpu_mask() and on_each_cpu(), which means these functions won't broadcast the operations to other CPUs when they're offline. In any case, if you think that we broadcast every operation to all CPUs, you're mistaken - TLB and cache ops are broadcast to only those CPUs which the thread is running on, or in the case of non-MM specific, to all online CPUs. So the only thing we have to worry about is "is there an ID register available" which is covered by the is_smp() test. Checking the CPU mask is far more expensive and imho ends up needlessly adding to the complexity. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
