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AJvYcCWYkNgF2/WBRishWkiQlgNTl2DXpQUQ2QrtlvX4UQACN4+n3QFYSmpCth09JuLtIm07cGQOFYlb4Q==@kvack.org X-Gm-Message-State: AOJu0YyTMZNFQfy2Zl23s5Izs7b/bwhwIZ5k3nqoM9FrE94sP+9m4D1t ybl3nMtsYjvQsENtGXN8CNMgqHwjA5RCdDFCX5Af5XO0ZPhHlEFWB8PPVund+VTDYCbN4LmGAp/ 8WBNu8mquWJ8lHgpxg4NGlzhEBhoLn2D3N7AvRDqSHQ== X-Gm-Gg: ASbGncvR9eAzQ4j0jR3tPOUqyqH9ekAEE4nXJ1keFbFEeMRXNMoVfVcx2QH2nZ+t0Ng m3PyqXYRY8Avv8Tp1oV4IN81alnxqylNFJlhbyGZ6Pr53CobuUybLtn0QYaxx3lONnY4yzUocka 56IZ7kfQbd81boVDVwvGN3BrWO64Wy6h3YcFG1EBo70IMQHA== X-Google-Smtp-Source: AGHT+IHRyVkZ57nzhyTKCltTrLPpMwsHIDQ7uc0ufm1hakxjYl3N48OH2yPl7P6OWGuq8y5vu9wPIRf0jtP4zFgzCA0= X-Received: by 2002:a05:6830:730d:b0:739:f13a:6f41 with SMTP id 46e09a7af769-73cf06820a7mr1087123a34.25.1752119117879; Wed, 09 Jul 2025 20:45:17 -0700 (PDT) MIME-Version: 1.0 References: <20250704084500.62688-1-cuiyunhui@bytedance.com> In-Reply-To: From: yunhui cui Date: Thu, 10 Jul 2025 11:45:06 +0800 X-Gm-Features: Ac12FXyE0pTXhJgf-CmJFYzzVTnilQd8t8nNTo1YCw7wwl6W4gnmmliWfCBZFlE Message-ID: Subject: Re: [External] [PATCH] RISC-V: store percpu offset in CSR_SCRATCH To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Cc: masahiroy@kernel.org, nathan@kernel.org, nicolas.schier@linux.dev, dennis@kernel.org, tj@kernel.org, cl@gentwo.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, andybnac@gmail.com, bjorn@rivosinc.com, cyrilbur@tenstorrent.com, rostedt@goodmis.org, puranjay@kernel.org, ben.dooks@codethink.co.uk, zhangchunyan@iscas.ac.cn, ruanjinjie@huawei.com, jszhang@kernel.org, charlie@rivosinc.com, cleger@rivosinc.com, antonb@tenstorrent.com, ajones@ventanamicro.com, debug@rivosinc.com, haibo1.xu@intel.com, samuel.holland@sifive.com, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-riscv , wangziang.ok@bytedance.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 11ED01C0009 X-Rspamd-Server: rspam09 X-Stat-Signature: uw54jyfu7da97gqparun9hhg6ez9eegw X-HE-Tag: 1752119118-3127 X-HE-Meta: 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 PFTBPn+d rJouBiY6G8bGByc3qqMJXPUU9YyF8rlqoY/o5FOZ0/L8yRP5BbQwwujyJQ41Tqv3tceU2RhH7B5Yax5EV8JjZ55281ZSf4cc3Pm90GQnbvHTPEmOy1Z9z2xwRw0ax4K+xUY+bzI8omy22g0n+hqlSRm8ZW78zo6ef7rRQoMp3YjuXS91b7JGe0/0pryuCTEcJDxlteQO2YPHWcakXD/7blSdhytCshPxAH6P/1mLPtdBHHN2DE8XwgK1Y4fjcfvF7U5caixf62wqIHOI449y6vDKoPgr0AgR+QWEJQIgwHAz2mu71kUhFDLGz8sSX6JVV+WZV8+08hqHvoaIuf9hBR6qq9G7D0vz0LCwrJUAQiTjO4F2LxW39kFA0SiqIUAOL32zGqm7WjLFPKvHXohqsS6IziQ== 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: Hi Radim, On Wed, Jul 9, 2025 at 10:20=E2=80=AFPM Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > > 2025-07-09T19:42:26+08:00, yunhui cui : > > Bench platform: Spacemit(R) X60 > > No changes: > > 6.77, 6.791, 6.792, 6.826, 6.784, 6.839, 6.776, 6.733, 6.795, 6.763 > > Geometric mean: 6.786839305 > > Reusing the current scratch: > > 7.085, 7.09, 7.021, 7.089, 7.068, 7.034, 7.06, 7.062, 7.065, 7.051 > > Geometric mean: 7.062466876 > > Great results. > > > A degradation of approximately 4.06% is observed. The possible cause > > of the degradation is that the CSR_TVEC register is set every time a > > kernel/user exception occurs. > > I assume the same. > > > The following is the patch without percpu optimization, which only > > tests the overhead of separating exceptions into kernel and user > > modes. > > Is the overhead above with this patch? And when we then use the > CSR_SCRATCH for percpu, does it degrade even further? > > Thanks. We can see that the percpu optimization is around 2.5% through the method of fixing registers, and we can consider that the percpu optimization can bring a 2.5% gain. Is there no need to add the percpu optimization logic on the basis of the scratch patch for testing? Reference: https://lists.riscv.org/g/tech-privileged/message/2485 Thanks, Yunhui