Re: [PATCH 1/5] irq_work: Architecture support for remote irq work raise

[Peter Zijlstra]

On Mon, May 12, 2014 at 01:33:53AM +0200, Frederic Weisbecker wrote:
> We are going to extend irq work to support remote queuing.
> 
> So lets add a cpu argument to arch_irq_work_raise(). The architectures
> willing to support that must then provide the backend to raise irq work
> IPIs remotely.
> 
> Initial support is provided for x86 and ARM since they are easily
> extended. The other archs that overwrite arch_irq_work_raise() seem
> to use local clock interrupts and therefore need deeper rewrite of their
> irq work support to implement remote raising.
> 

> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>

Why not borrow the smp_call_function IPI for the remote bits? We could
limit the 'safe from NMI' to the local works. And we validate this by
putting a WARN_ON(in_nmi()) in irq_work_queue_on().

At some later stage we could look at maybe merging the smp_function_call
and irq_work into a single thing, where we have the irq_work interface
as async and the smp_function_call() as sync interface.

But for now a quick 'hack' would be to call __irq_work_run() from
generic_smp_call_function_single_interrupt().

That would leave arch_irq_work_raise() as the special NMI safe local IPI
hook.

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