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Thu, 01 Feb 2024 07:03:53 -0800 (PST) X-Forwarded-Encrypted: i=0; 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 Received: from andrea ([31.189.34.185]) by smtp.gmail.com with ESMTPSA id bk7-20020a0560001d8700b0033addbf2d2csm16043387wrb.9.2024.02.01.07.03.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Feb 2024 07:03:52 -0800 (PST) Date: Thu, 1 Feb 2024 16:03:48 +0100 From: Andrea Parri To: Alexandre Ghiti Cc: Catalin Marinas , Will Deacon , Thomas Bogendoerfer , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Paul Walmsley , Palmer Dabbelt , Albert Ou , Andrew Morton , Ved Shanbhogue , Matt Evans , Dylan Jhong , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH RFC/RFT v2 4/4] riscv: Stop emitting preventive sfence.vma for new userspace mappings with Svvptc Message-ID: References: <20240131155929.169961-1-alexghiti@rivosinc.com> <20240131155929.169961-5-alexghiti@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240131155929.169961-5-alexghiti@rivosinc.com> X-Rspamd-Queue-Id: 4672D4004D X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: d5ezjsi76qwo5kh8m7h6rxsrbm6ukfhp X-HE-Tag: 1706799835-40536 X-HE-Meta: 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 DCeOrWYZ xIay14HOZp7Nq1dymBhu3MF7xxOPNpCiPVbhl7bgX6/eU1koirknJuw03wOK5BOsFYVz0psEmEo5ke3GAFvwZZMRn4HTfCcO7YwyoBRWbIoLqm4ygkIByTMkSmj890uVocFLzm45C8Y95rR5iVtXVWg86SaTwXYrAFff/vmvOcUtbnL53m81QE5djbVxZwTrcfKblxCpN191zRDb36WSbazmeoRQocvHJAcw5W6GuoQKTUPy2HRYaAkOEzsPV2BkObvj1MlRN646igzLN+EejEeLcjwSw/PDNLsxMTyhWet7lnNaau0P24U90B2L0uF70uB1n6Q5MasnXovopHhoV0NNvD6Ea4Nerke8FN5Ewf1Js8I5S0WxkFWfnRQ76ThkZLPB2d7ow1unSICJFxQMwkpRTnWGegWu0crI78HY0YWw9intZ0KyGkOiUjPN+WZzZYPX7a+vGylJNKt2B1Wv7Wq6aV/NRMoUACz6OWFbLop6wj3w= 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: List-Subscribe: List-Unsubscribe: On Wed, Jan 31, 2024 at 04:59:29PM +0100, Alexandre Ghiti wrote: > The preventive sfence.vma were emitted because new mappings must be made > visible to the page table walker but Svvptc guarantees that xRET act as > a fence, so no need to sfence.vma for the uarchs that implement this > extension. AFAIU, your first submission shows that you don't need that xRET property. Similarly for other archs. What was rationale behind this Svvptc change? > This allows to drastically reduce the number of sfence.vma emitted: > > * Ubuntu boot to login: > Before: ~630k sfence.vma > After: ~200k sfence.vma > > * ltp - mmapstress01 > Before: ~45k > After: ~6.3k > > * lmbench - lat_pagefault > Before: ~665k > After: 832 (!) > > * lmbench - lat_mmap > Before: ~546k > After: 718 (!) This Svvptc seems to move/add the "burden" of the synchronization to xRET: Perhaps integrate the above counts w/ the perf gains in the cover letter? Andrea