From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BDBFA192598 for ; Fri, 18 Jul 2025 02:32:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752805928; cv=none; b=YswUK6EwjKEt0h4MvLqusc2r+UDNrtf203VKaX8BZ7nJ+43PV8ggWp7mkoJgsVYATs3yKMeadXyY/wQrsBCPABASMtl4rMOk2lpLys9TZ8p5XaFrjeNT8nzfworcDzyZHkkoXZv+5FeD0G8GcrsPUWInehpb3D4GOYrYMMBgmzg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752805928; c=relaxed/simple; bh=R9OH3vIsRbQ2qkCL2Wec5pMYKZZY7OAwuWLWAc7X/1U=; h=Message-ID:Date:MIME-Version:To:CC:From:Subject:Content-Type; b=u+49e6cFRpOf97f7ql3IdfB5pGuTZmBoMCUmwpiOWw0UxxowhSAZ80Pu9OWA4ijSB/A3rElY9pQ2lU2xNJ+vvfdkbcvxBAgqmsHmCl4DAIrq94gEQO1Oe651yoGIBEt4QwO8rl33z1pph/HJcFwzmr3lIjGHfbhbZi8bU/YQ/9I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.194]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4bjtyv2YnFzvPtk; Fri, 18 Jul 2025 10:29:11 +0800 (CST) Received: from dggemv705-chm.china.huawei.com (unknown [10.3.19.32]) by mail.maildlp.com (Postfix) with ESMTPS id 78150140279; Fri, 18 Jul 2025 10:32:01 +0800 (CST) Received: from kwepemq200011.china.huawei.com (7.202.195.155) by dggemv705-chm.china.huawei.com (10.3.19.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 18 Jul 2025 10:32:01 +0800 Received: from [10.67.110.108] (10.67.110.108) by kwepemq200011.china.huawei.com (7.202.195.155) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 18 Jul 2025 10:32:00 +0800 Message-ID: <24afb8de-622a-4865-bd8e-8e89ccfff8f4@huawei.com> Date: Fri, 18 Jul 2025 10:32:00 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: , , , , , , , , , , ruanjinjie CC: , From: "Liao, Chang" Subject: [RFC] SCTLR_EL1.TIDCP toggling for performance Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To kwepemq200011.china.huawei.com (7.202.195.155) 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 -- BR Liao, Chang