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Date:   Tue, 27 Sep 2022 11:46:38 +0530
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Subject: Re: [PATCH v4 2/2] arm64: support batched/deferred tlb shootdown
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To:     Yicong Yang <yangyicong@huawei.com>, akpm@linux-foundation.org,
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References: <20220921084302.43631-1-yangyicong@huawei.com>
 <20220921084302.43631-3-yangyicong@huawei.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
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[...]

On 9/21/22 14:13, Yicong Yang wrote:
> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> +{
> +	/* for small systems with small number of CPUs, TLB shootdown is cheap */
> +	if (num_online_cpus() <= 4)

It would be great to have some more inputs from others, whether 4 (which should
to be codified into a macro e.g ARM64_NR_CPU_DEFERRED_TLB, or something similar)
is optimal for an wide range of arm64 platforms.

> +		return false;> +
> +#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI
> +	if (unlikely(this_cpu_has_cap(ARM64_WORKAROUND_REPEAT_TLBI)))
> +		return false;
> +#endif
> +
> +	return true;
> +}
> +

[...]