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SubjectRe: [PATCH v3 1/9] smp: Run functions concurrently in smp_call_function_many()
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> On Jul 22, 2019, at 11:16 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Jul 19, 2019 at 11:23:06AM -0700, Dave Hansen wrote:
>> On 7/18/19 5:58 PM, Nadav Amit wrote:
>>> @@ -624,16 +622,11 @@ EXPORT_SYMBOL(on_each_cpu);
>>> void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
>>> void *info, bool wait)
>>> {
>>> - int cpu = get_cpu();
>>> + preempt_disable();
>>>
>>> - smp_call_function_many(mask, func, info, wait);
>>> - if (cpumask_test_cpu(cpu, mask)) {
>>> - unsigned long flags;
>>> - local_irq_save(flags);
>>> - func(info);
>>> - local_irq_restore(flags);
>>> - }
>>> - put_cpu();
>>> + __smp_call_function_many(mask, func, func, info, wait);
>>> +
>>> + preempt_enable();
>>> }
>>
>> The get_cpu() was missing it too, but it would be nice to add some
>> comments about why preempt needs to be off. I was also thinking it
>> might make sense to do:
>>
>> cfd = get_cpu_var(cfd_data);
>> __smp_call_function_many(cfd, ...);
>> put_cpu_var(cfd_data);
>>
>> instead of the explicit preempt_enable/disable(), but I don't feel too
>> strongly about it.
>
> It is also required for cpu hotplug.

But then smpcfd_dead_cpu() will not respect the “cpu” argument. Do you still
prefer it this way (instead of the current preempt_enable() /
preempt_disable())?
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