Re: [PATCH v2 0/2] send tlb_remove_table_smp_sync IPI only to necessary CPUs

Peter Zijlstra
2023-06-21T07:44:35Z

On Tue, Jun 20, 2023 at 05:46:16PM +0300, Yair Podemsky wrote:
> Currently the tlb_remove_table_smp_sync IPI is sent to all CPUs
> indiscriminately, this causes unnecessary work and delays notable in
> real-time use-cases and isolated cpus.
> By limiting the IPI to only be sent to cpus referencing the effected
> mm.
> a config to differentiate architectures that support mm_cpumask from
> those that don't will allow safe usage of this feature.
>
> changes from -v1:
> - Previous version included a patch to only send the IPI to CPU's with
> context_tracking in the kernel space, this was removed due to race
> condition concerns.
> - for archs that do not maintain mm_cpumask the mask used should be
> cpu_online_mask (Peter Zijlstra).
>

Would it not be much better to fix the root cause? As per the last time,
there's patches that cure the thp abuse of this.