From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15E8FC433FE for ; Tue, 15 Nov 2022 03:34:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 789ED6B0072; Mon, 14 Nov 2022 22:34:51 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 711786B0073; Mon, 14 Nov 2022 22:34:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5D97F8E0002; Mon, 14 Nov 2022 22:34:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 4E8D06B0072 for ; Mon, 14 Nov 2022 22:34:51 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 23F551A0F4F for ; Tue, 15 Nov 2022 03:34:51 +0000 (UTC) X-FDA: 80134259982.01.A4FBC77 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf18.hostedemail.com (Postfix) with ESMTP id 6B4C91C0003 for ; Tue, 15 Nov 2022 03:34:48 +0000 (UTC) Received: from canpemm500009.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4NBBXf463pzqSRP; Tue, 15 Nov 2022 11:30:58 +0800 (CST) Received: from [10.67.102.169] (10.67.102.169) by canpemm500009.china.huawei.com (7.192.105.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 15 Nov 2022 11:34:44 +0800 CC: , , , , , , , , , , , , , , , , , Barry Song <21cnbao@gmail.com>, , , , Barry Song , Nadav Amit , Mel Gorman Subject: Re: [PATCH v5 2/2] arm64: support batched/deferred tlb shootdown during page reclamation To: Anshuman Khandual , , , , , , , References: <20221028081255.19157-1-yangyicong@huawei.com> <20221028081255.19157-3-yangyicong@huawei.com> <86fbdc8c-0dcb-9b8f-d843-63460d8b1d6a@arm.com> <9982dac0-9f2e-112a-d440-467c8e8f8aa4@huawei.com> <40f1b5ad-2165-bb81-1ff5-89786373fa14@arm.com> From: Yicong Yang Message-ID: <5bbd5364-fcec-5fc2-4780-e9b44f2ab135@huawei.com> Date: Tue, 15 Nov 2022 11:34:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <40f1b5ad-2165-bb81-1ff5-89786373fa14@arm.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.102.169] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500009.china.huawei.com (7.192.105.203) X-CFilter-Loop: Reflected ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668483289; a=rsa-sha256; cv=none; b=dpLciEtOMUSAptnb/FVXJTkjO9LcDBXEaKBXkrGO+cyTeFpBjx27nq9Z3s12ID3AaIic8f Gs8r6bOoui99fXNMakqfIFmha9bcwrxlANXkRWDbDJzcztkdBFyY0IeC3y8b1qqtL+4/zq E20md0XEHy93i0FlTSi8M1SSC0PzhYY= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf18.hostedemail.com: domain of yangyicong@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=yangyicong@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668483289; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZBhHa7YYDofuS0iS62r9AiKymhEby/I/Vx6GQ/PfJXs=; b=D5JzdPO+D/a+nw/OMceH6lSusEv8zScswr2+YeRdo3S5XVulp0GFKtAwaMkMFGxQQSLNf8 zUxDwT5XNl5Wxe7QiIR4YsCe5+FBoQG0yU5B0sv0OzUQS/TW9v/DNb8CFE63pd6TX+bj+T 3frVmuL8lntwMvjU4qSqX4335InhwnA= X-Rspam-User: X-Stat-Signature: mdcuhw3pdy6p13fh5szrydfum3gn5k8f X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6B4C91C0003 Authentication-Results: imf18.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf18.hostedemail.com: domain of yangyicong@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=yangyicong@huawei.com X-HE-Tag: 1668483288-606030 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/11/14 22:19, Anshuman Khandual wrote: > > > On 11/14/22 14:16, Yicong Yang wrote: >> On 2022/11/14 11:29, Anshuman Khandual wrote: >>> >>> On 10/28/22 13:42, Yicong Yang wrote: >>>> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) >>>> +{ >>>> + /* >>>> + * TLB batched flush is proved to be beneficial for systems with large >>>> + * number of CPUs, especially system with more than 8 CPUs. TLB shutdown >>>> + * is cheap on small systems which may not need this feature. So use >>>> + * a threshold for enabling this to avoid potential side effects on >>>> + * these platforms. >>>> + */ >>>> + if (num_online_cpus() <= CONFIG_ARM64_NR_CPUS_FOR_BATCHED_TLB) >>>> + return false; >>>> + >>>> +#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI >>>> + if (unlikely(this_cpu_has_cap(ARM64_WORKAROUND_REPEAT_TLBI))) >>>> + return false; >>>> +#endif >>> should_defer_flush() is immediately followed by set_tlb_ubc_flush_pending() which calls >>> arch_tlbbatch_add_mm(), triggering the actual TLBI flush via __flush_tlb_page_nosync(). >>> It should be okay to check capability with this_cpu_has_cap() as the entire call chain >>> here is executed on the same cpu. But just wondering if cpus_have_const_cap() would be >>> simpler, consistent, and also cost effective ? >>> >> ok. Checked cpus_have_const_cap() I think it matches your words. >> >>> Regardless, a comment is needed before the #ifdef block explaining why it does not make >>> sense to defer/batch when __tlbi()/__tlbi_user() implementation will execute 'dsb(ish)' >>> between two TLBI instructions to workaround the errata. >>> >> The workaround for the errata mentioned the affected platforms need the tlbi+dsb to be done >> twice, so I'm not sure if we defer the final dsb will cause any problem so I think the judgement >> here is used for safety. I have no such platform to test if it's ok to defer the last dsb. > > We should not defer TLB flush on such systems, as ensured by the above test and 'false' > return afterwards. The only question is whether this decision should be taken at a CPU > level (which is affected by the errata) or the whole system level. > > What is required now > > - Replace this_cpu_has_cap() with cpus_have_const_cap ? > - Add the following comment before the #ifdef check > Have respin the series according to the above comments: https://lore.kernel.org/lkml/20221115031425.44640-3-yangyicong@huawei.com/ Thanks. > /* > * TLB flush deferral is not required on systems, which are affected with > * ARM64_WORKAROUND_REPEAT_TLBI, as __tlbi()/__tlbi_user() implementation > * will have two consecutive TLBI instructions with a dsb(ish) in between > * defeating the purpose (i.e save overall 'dsb ish' cost). > */ > > . >