linux-kernel - Re: [RFC] SCTLR_EL1.TIDCP toggling for performance

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Message-ID: <1b17f637-ecba-43cc-8ca6-e4bb73bd152e@huawei.com>
Date: Tue, 22 Jul 2025 09:47:30 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Kristina Martšenko <kristina.martsenko@....com>
CC: <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, <catalin.marinas@....com>,
	<will@...nel.org>, <mark.rutland@....com>, <sashal@...nel.org>,
	<yangjiangshui@...artners.com>, <zouyipeng@...wei.com>, <justin.he@....com>,
	<zengheng4@...wei.com>, <yangyicong@...ilicon.com>, ruanjinjie
	<ruanjinjie@...wei.com>
Subject: Re: [RFC] SCTLR_EL1.TIDCP toggling for performance



在 2025/7/19 1:28, Kristina Martšenko 写道:
> Hi Chang,
> 
> On 18/07/2025 03:32, Liao, Chang wrote:
>> Hi, Kristina
>>
>> I've reviewed your patch [1] for FEAT_TIDCP1 support, which by default traps EL0
>> accesses to implementation-defined system registers and instructions at EL1/EL2.
>>
>> Do you have any plans to add support for toggling the SCTLR_EL1.TIDCP1 bit? I'm
>> encountering performance degradation on CPU where certain implementation-defined
>> registers and instructions are designed for EL0 performance use. The trapping
>> overhead is substantial enough to compromise any benefits, and it's even worse
>> in virtualization. Therefore, I'm hoping there's a way to clear the SCTLR_EL1.TIDCP1
>> bit on such platforms, perhaps via a kernel config option or command-line parameter.
>> Alternatively, do you have a better solution for gracefully toggling this bit on
>> and off?
>>
>> Thanks
>>
>> [1] https://lore.kernel.org/linux-arm-kernel/Yrw3NWkH6D0CgRsF@sirena.org.uk/T/#m5cfdb27b48d9d7e30db73e991fc6c232ba8a7349
> 
> I don't have any plans to add support for toggling it. You could try sending a
> patch for a Kconfig option or kernel command-line parameter. I'm not really

Kristina, I am going to send a patch for command-line paramter as Catalin suggested.

Thanks.

> sure what the maintainers' view on supporting IMP-DEF features is.
> 
> Thanks,
> Kristina
> 
> 

-- 
BR
Liao, Chang