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Thu, 27 Oct 2022 10:42:08 +0000 (UTC) X-FDA: 80066389536.23.0EEE257 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf15.hostedemail.com (Postfix) with ESMTP id A4592A0037 for ; Thu, 27 Oct 2022 10:42:07 +0000 (UTC) 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: Content-Type: text/plain; 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dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf15.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com X-Stat-Signature: aoodrznigfwf4615ahg9rb7ge94qjz8e X-HE-Tag: 1666867327-129330 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 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 ?