Re: [PATCH v6 1/9] smp: Run functions concurrently in smp_call_function_many_cond()

[Nadav Amit]

> On Mar 1, 2021, at 9:10 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> On Sat, Feb 20, 2021 at 03:17:04PM -0800, Nadav Amit wrote:
>> +		/*
>> +		 * 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.
>> +		 */
>> +		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);
> 
> I just ran into conflicts with another patch set, and noticed that the
> above should probably be:
> 
> 		if (nr_cpus == 1)
> 			send_call_function_single_ipi(last_cpu);
> 		else if (likely(nr_cpus > 1))
> 			arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
> 
> Which will avoid the IPI when @last_cpu is idle.

Good point. Makes one wonder whether all these inter-core communication
(through cpu_tlbstate.is_lazy, csd->node.llist and ti->flags) are
really necessary or can be combined.

Well, that’s for later I presume.