On 01/05/2013 04:06 PM, Russell King - ARM Linux wrote:

On Thu, Jan 03, 2013 at 06:58:38PM -0800, Srivatsa Vaddagiri wrote:

quoted

I also think that the
wait_for_completion() based wait in ARM's __cpu_die() can be replaced with a
busy-loop based one, as the wait there in general should be terminated within
few cycles.

Why open-code this stuff when we have infrastructure already in the kernel
for waiting for stuff to happen?  I chose to use the standard infrastructure
because its better tested, and avoids having to think about whether we need
CPU barriers and such like to ensure that updates are seen in a timely
manner.

My stance on a lot of this idle/cpu dying code is that much of it can
probably be cleaned up and merged into a single common implementation -
in which case the use of standard infrastructure for things like waiting
for other CPUs do stuff is even more justified.

On similar lines, Nikunj (in CC) and I had posted a patchset sometime ago to
consolidate some of the CPU hotplug related code in the various architectures
into a common standard implementation [1].

However, we ended up hitting a problem with Xen, because its existing code
was unlike the other arch/ pieces [2]. At that time, we decided that we will
first make the CPU online and offline paths symmetric in the generic code and
then provide a common implementation of the duplicated bits in arch/, for the
new CPU hotplug model [3].

I guess we should probably revisit it sometime, consolidating the code in
incremental steps if not all at a time...

--
[1]. http://lwn.net/Articles/500185/
[2]. http://thread.gmane.org/gmane.linux.kernel.cross-arch/14342/focus=14430
[3]. http://thread.gmane.org/gmane.linux.kernel.cross-arch/14342/focus=15567

Regards,
Srivatsa S. Bhat