linux-kernel - Re: [PATCH v4 2/2] arm64: support batched/deferred tlb shootdown during page reclamation

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Message-ID: <8e391962-4e3a-5a56-64b4-78e8637e3b8c@huawei.com>
Date:   Tue, 27 Sep 2022 17:15:40 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
CC:     <yangyicong@...ilicon.com>, <corbet@....net>,
        <peterz@...radead.org>, <arnd@...db.de>,
        <linux-kernel@...r.kernel.org>, <darren@...amperecomputing.com>,
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        <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] arm64: support batched/deferred tlb shootdown
 during page reclamation

On 2022/9/27 14:16, Anshuman Khandual wrote:
> [...]
> 
> 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.
> 

Do you prefer this macro to be static or make it configurable through kconfig then
different platforms can make choice based on their own situations? It maybe hard to
test on all the arm64 platforms.

Thanks.

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