Is Pandaboard cpuhotplug working stably?
Russell King - ARM Linux
linux at arm.linux.org.uk
Thu Dec 22 05:24:54 EST 2011
On Thu, Dec 22, 2011 at 02:19:23PM +0530, Shilimkar, Santosh wrote:
> + Peter Z
> On Wed, Dec 21, 2011 at 3:37 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Wed, Dec 21, 2011 at 05:59:07PM +0800, Barry Song wrote:
> >> 2011/12/21 Russell King - ARM Linux <linux at arm.linux.org.uk>:
> >> > cpu hotplug is basically totally buggered - the preconditions placed
> >> > upon the bringup code path are basically impossible to satisfy in any
> >> > shape or form at the moment.
> >> >
> >> > There's the requirement that the secondary CPU is marked online and
> >> > active before interrupts are enabled for the thread migration stuff
> >> > to behave correctly. However, this is incompatible with smp_call_function()
> >> > which will wait for online CPUs to respond to an IPI - which this one
> >> > won't because interrupts are disabled.
> >> >
> >> > I think there was some discussion about how to fix this but I don't
> >> > recall the details.
> >> thanks, Russell. then could i think this is an ARM-kernel-specific bug
> >> which exists on all ARM SMP chips for the moment?
> >> and that bug doesn't happen on x86:
> > I don't think so. There's nothing ARM specific about it.
> There are few patches floating around for this issue. I posted one version
> long back  and then there was one more form Thomas G.
> The most recent is from one is from Peter Z  which is moving the
> fix for the cup online race to core code.
> Can you try Peter's patch with your test-case ?
>  https://lkml.org/lkml/2011/6/20/79
>  https://lkml.org/lkml/2011/12/15/255
 is already fixed - and is not the latest "problem" with this code.
Fixing the problem in  actually itself created the latest problem
with smp_call_function() which wasn't there before this change. Patch
 refers to this problem and proposes a fix for it.
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