Messages in this thread Patch in this message | | | Date | Mon, 22 Jul 2019 21:34:14 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 1/9] smp: Run functions concurrently in smp_call_function_many() |
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On Mon, Jul 22, 2019 at 06:41:44PM +0000, Nadav Amit wrote: > > 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())?
I just meant that the preempt_disable() (either form) is required for hotplug (we must not send IPIs to offline CPUs, that gets things upset).
Personally I don't mind the bare preempt_disable() as you have; but I think Dave's idea of a comment has merrit.
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