linux-kernel - Re: [PATCH v2 0/2] send tlb_remove_table_smp

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Message-ID: <20230621074337.GF2046280@hirez.programming.kicks-ass.net>
Date:   Wed, 21 Jun 2023 09:43:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yair Podemsky <ypodemsk@...hat.com>
Cc:     mtosatti@...hat.com, ppandit@...hat.com, david@...hat.com,
        linux@...linux.org.uk, mpe@...erman.id.au, npiggin@...il.com,
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Subject: Re: [PATCH v2 0/2] send tlb_remove_table_smp_sync IPI only to
 necessary CPUs

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.