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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3A206C38A2D for ; Thu, 27 Oct 2022 10:43:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:References:Cc:To:Subject: From:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=V68cm1cY2VEcW5ci4RiqVWWFZwdPsOm54A2X3YOmkQY=; b=q8qkQ2sDdBsZUP SFdvFXihnwcQWaY9Meqdi7T+bT2DlGjGfhXbXlI7CIQ+G1/r5sKAVab8ctYZ8s4E/u6mF8R31R6yy Ku38jq4U95c3+3am7zpe5qBMiKMXqHRiiMtbYT2rcNSvYuNcXg32VyP4M2Pbd4bee8aRGZyGev9j8 bLFz4Y41PwK0QL6BaopUxOyJav+/kO1IkSg8a/yTQ5JyJ6hFoM/zT4rumezUUyOkE/8ao6J6qfzuI f5Mo5X60nzVSFwipgqphi8TDYgHugYu79JaqlwUKWu//OoLP7Up4Eu7T0++BJ/1blyQc0ORxIZOPK AR/x4gSz5Y4QfQSsGbaQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oo0L4-00Cv4u-BM; Thu, 27 Oct 2022 10:42:18 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oo0Ky-00Cv2H-MZ; Thu, 27 Oct 2022 10:42:16 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BF9221FB; Thu, 27 Oct 2022 03:42:12 -0700 (PDT) Received: from [10.163.38.26] (unknown [10.163.38.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2EF8D3F445; Thu, 27 Oct 2022 03:41:56 -0700 (PDT) Message-ID: Date: Thu, 27 Oct 2022 16:11:59 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 From: Anshuman Khandual Subject: Re: [PATCH v4 2/2] arm64: support batched/deferred tlb shootdown during page reclamation To: Barry Song <21cnbao@gmail.com>, Yicong Yang Cc: yangyicong@hisilicon.com, corbet@lwn.net, peterz@infradead.org, arnd@arndb.de, linux-kernel@vger.kernel.org, darren@os.amperecomputing.com, huzhanyuan@oppo.com, lipeifeng@oppo.com, zhangshiming@oppo.com, guojian@oppo.com, realmz6@gmail.com, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, akpm@linux-foundation.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, wangkefeng.wang@huawei.com, xhao@linux.alibaba.com, prime.zeng@hisilicon.com, Barry Song , Nadav Amit , Mel Gorman , catalin.marinas@arm.com, will@kernel.org, linux-doc@vger.kernel.org References: <20220921084302.43631-1-yangyicong@huawei.com> <20220921084302.43631-3-yangyicong@huawei.com> <168eac93-a6ee-0b2e-12bb-4222eff24561@arm.com> <8e391962-4e3a-5a56-64b4-78e8637e3b8c@huawei.com> Content-Language: en-US In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221027_034212_792351_41B09267 X-CRM114-Status: GOOD ( 20.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 9/28/22 05:53, Barry Song wrote: > On Tue, Sep 27, 2022 at 10:15 PM Yicong Yang wrote: >> >> 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. >>> > > I have tested it on a 4-cpus and 8-cpus machine. but i have no machine > with 5,6,7 > cores. > I saw improvement on 8-cpus machines and I found 4-cpus machines don't need > this patch. > > so it seems safe to have > if (num_online_cpus() < 8) > >> >> 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. > > Maybe we can have this default enabled on machines with 8 and more cpus and > provide a tlbflush_batched = on or off to allow users enable or > disable it according > to their hardware and products. Similar example: rodata=on or off. No, sounds bit excessive. Kernel command line options should not be added for every possible run time switch options. > > Hi Anshuman, Will, Catalin, Andrew, > what do you think about this approach? > > BTW, haoxin mentioned another important user scenarios for tlb bach on arm64: > https://lore.kernel.org/lkml/393d6318-aa38-01ed-6ad8-f9eac89bf0fc@linux.alibaba.com/ > > I do believe we need it based on the expensive cost of tlb shootdown in arm64 > even by hardware broadcast. Alright, for now could we enable ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH selectively with CONFIG_EXPERT and for num_online_cpus() > 8 ? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel