[PATCH] arm64: smp: Add a memory barrier before we start secondary cores

[Catalin Marinas]

On 12 Feb 2014, at 14:56, Mark Brown <broonie at kernel.org> wrote:

> On Wed, Feb 12, 2014 at 01:43:32PM +0000, Catalin Marinas wrote:
> 
>> I think we can drop this until Vincent clarifies the synchronisation
>> requirements (still wondering whether spinlocks are needed).
> 
> Even if they're not actually required for the topology code the fact
> that we're having to think about what is needed suggests that the code
> is going to end up being clearer and hence more maintainable going
> forwards if we add it.

I think we should aim to understand the code better rather than just
adding the spinlocks. Some simple questions:

- Who uses the topology information and when? (the scheduler? first time after or
before secondaries are started?)

- Who updates the topology information? (primary and secondary startup
code?)

- What about hotplug?

- Can any of the above happen in parallel on different CPUs?

Catalin