Re: [RFC PATCH 3/6] smp: Run functions concurrently in smp_call_function_many()

[Peter Zijlstra]

> +		/*
> +		 * Choose the most efficient way to send an IPI. Note that the
> +		 * number of CPUs might be zero due to concurrent changes to the
> +		 * provided mask or cpu_online_mask.
> +		 */

Since we have preemption disabled here, I don't think online mask can
shrink, cpu-offline uses stop_machine().

> +		if (nr_cpus == 1)
> +			arch_send_call_function_single_ipi(last_cpu);
> +		else if (likely(nr_cpus > 1))
> +			arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
> +	}