From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.221.42 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794173578; b=ZJXBkJfERajjRZu/+TB+IUDtHUW1y/519yVAEwINC2prLn8fIW68mXhQibHl8hjij6pZ pgDw8i32cZqGIKDcGQNcKyC1JWmDuzjPMQv+RtocoF1xxff0jpb7yEh4qI0lq0Ya6yxJ1 micUSvfO+pZf2ST+F89JnPw7AtanuPGxunOLuRdDOvQdDKi9U8UJupWsjGhr6JcPMuyk/ 1TrIV9M1oeQXfznZwD3dHq9XRD+Zpz0sai8KhABNXQInB45eCxphPyZe0OTa84O/YrjnP GwLCT3cnOaz0Ck8Nw+GJauACbR06N+Bf3srcr54YRkXoLrX5Ma7ETjERmMrsgKJqU+w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794173578; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=2zV+j1o90j03z3/bSKQRAMr2OAwRnzRNXDWN23pKxKc=; b=xzJ04v8GecShNOeJJUUBuhN4TcN7izN4W3jB07/qXW960SgiBaix7AImfd+kM6s6GD21 wefEYn44NJ8NSdUzYyv4C/VpMN+XskFSrXP/yqUz0LvMH5HTBpHLb0AhyxcU48rXkOvwt R7llbNX4vGPcOVqMLHG0QMe4d+ANgYNuqk93+BOZPS40Zvod417wAkqtGaFY+Sa1JmbF+ e8UcVDv83RB6bW8YwtniT0L10GQa06121FcOtrqlbCQTQi0A+CAWtjCHR/J3rThEML8mL s2AO9qQMEFVshhXTRRKBI8jQXrundgec0LmD8Vh9r1puqehZfWMoptbZk5nO6dvdI6A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=g1thKR+m; arc=none smtp.remote-ip=209.85.221.42 Received: from mail-wr1-f42.google.com (mail-wr1-f42.google.com [209.85.221.42]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F3D86606A31C for ; Sun, 8 Nov 2026 21:32:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org F3D86606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=g1thKR+m Received: by mail-wr1-f42.google.com with SMTP id ffacd0b85a97d-490d59c3edaso182160f8f.1 for ; Sun, 08 Nov 2026 13:32:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1794173576; x=1794778376; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=2zV+j1o90j03z3/bSKQRAMr2OAwRnzRNXDWN23pKxKc=; b=g1thKR+m3D3E2+c4hjI7QL3t50zazlEow2f3cU3NWSOcbViKGU+bFhuwrFyNJLKhd2 zHYXQnPFcPXe+OTWCNJAX5Doukw0IgV0+hx6/2omnjkeERyku7Qd1BPmTfG2Ec2vQYCj jBrOKkbpvQg6C2Qm/j7T6X8EjF/sd57iirCc6AnfscRPrdsjvNwASYBi0OE8oqXwYdCi zJl7umWLxRBDsqPH+gl3WB/UhcHVkpQHMEdZEB7hHpJ+Hv7UTPn8Nlv6LyoVls54rMcg mIo87yVqR5TSb6XzD5jEPo2n6Qli47aCR0sHQax0ubMztuUql/507jGMoGih3Wy2gIqR MqCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794173576; x=1794778376; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=2zV+j1o90j03z3/bSKQRAMr2OAwRnzRNXDWN23pKxKc=; b=GVeCB/k1QahlZpQOJnICqeNNUSp2TDSz+e8VKquzUX4OguOF3n3rTWagmT56Kx2LtT n19p5vSrbfzbxdT6N7PP3RxhZfGKQyudZekkYKgE7o9mYAoAQ8YVQZXmuHnuM5ahWYZQ WWDsTj7wV5Ye+SREKSdhSfC/rrbf5Lk3XYYrq1+05s1krXKdV1Uh0Djre3qGU8gD+uwY nppPDeCq7Qo3FYpNAleOH1mY3ZKHRh0xBJnQXsjT992Y/b9kzTN67ih9qI8ApHdfGyVH Fz8Z1/3FzVaXlfpxmgsnoVcHfT1f4N6lwAdbbmi6gFm44mGkxLK/Fbz2x4NtLPAdtwuG v09g== X-Forwarded-Encrypted: i=1; AL+hErEgbyRygxL2wb6Wss2DIatkv5hAzZ7x5dgPhP3feDjhLz14uJLHgWBhmFoHPtnvxkg8Nf0=@vger.kernel.org X-Gm-Message-State: APuU4Z+ePnoq0QL2sE8/v/14UpK7eHM1LqlbePk2lg8bTdd6r+rLm9iH LyGEc20IMgKgxhFeogOrEyS4UdQ0WBjmUxaXqK8VNDP3uy4qoqzwx50E X-Gm-Gg: AYBFou3p/S4e9yPbPUgRtHNLud/kIxCCA1iVFgdhK4+eaYIovotzgp13lM5UqcpGrdg iAWMbRU2Ll+4tM70S2ZArElEYP6EStcZimd3qFeKU8TELQNATW/TnzodaUtpff6hjVzBfS2a2OA LUcFZFg2yqU+tlP7WBfDkbLg+zVto718vEvKSZsFK9vrYxozeigki3pL7/97DtmxwnrwGZWknBc FtRb1O3ukejak5NkPoF/qnPgyHcnG/t8P5pANPjzNKp/9IZ39N7Qw3rdPqPhao0luhlNTet6Fmk dKu2JHlJgXVCw3WC9VjTzpjal2jPT/WS+C28Y4wtpEH/+DKH4STWHHNmSXcq1xYsyWoudVa+L1j HdHyLuqOC+GNYbb4vHsYaTzFdwqxM8TXyQ3L/bh91FdKpueDYQzPfHl9jXAK97qs+MXUVlO1xlT 4HMPQgSSpIo4+dD4AFUE0xbJyalZKPA16A6kNqtZaP3zqr8sVfy/vi3TqzfS4k/4WNJNZ1Bdf+Q ta3oeJLNfRvq22WBKnct1KxI+FZZlzGNL2y2ENmD4cWhwS4mdNIt0VUhZbAfg3xUdcFmgDESSwO XvHiexW8Iqf/dH9NeDTeARlaB6sPR1J2r1mcnmVHUggE4Gf47kJjISbVmDqM6bZt X-Received: by 2002:a05:6000:26c8:b0:48f:bbb5:61c2 with SMTP id ffacd0b85a97d-4958852d3b8mr5479500f8f.4.1794173576292; Sun, 08 Nov 2026 13:32:56 -0800 (PST) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49597371cc4sm5861840f8f.36.2026.11.08.13.32.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 13:32:56 -0800 (PST) Date: Sun, 8 Nov 2026 21:32:54 +0000 From: David Laight To: Yunhui Cui Cc: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, dennis@kernel.org, tj@kernel.org, cl@gentwo.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, bjorn@kernel.org, pulehui@huawei.com, puranjay@kernel.org, thuth@redhat.com, ajones@ventanamicro.com, ben.dooks@codethink.co.uk, rkrcmar@ventanamicro.com, samuel.holland@sifive.com, zong.li@sifive.com, conor.dooley@microchip.com, tglx@kernel.org, debug@rivosinc.com, seanwascoding@gmail.com, andybnac@gmail.com, menglong8.dong@gmail.com, cyrilbur@tenstorrent.com, wangruikang@iscas.ac.cn, atishp@rivosinc.com, apatel@ventanamicro.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, arnd@arndb.de, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com, qingfang.deng@siflower.com.cn, linux-arch@vger.kernel.org, llvm@lists.linux.dev, dave@stgolabs.net, emil@etsalapatis.com, ihor.solodrai@linux.dev, broonie@kernel.org Subject: Re: [PATCH v9 1/3] riscv: implement this_cpu operations Message-ID: <20261108213254.67805ef0@pumpkin> In-Reply-To: <20261108110406.97495-2-cuiyunhui@bytedance.com> References: <20261108110406.97495-1-cuiyunhui@bytedance.com> <20261108110406.97495-2-cuiyunhui@bytedance.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 8 Nov 2026 19:04:04 +0800 Yunhui Cui wrote: > RISC-V has no asm/percpu.h, so this_cpu_*() read-modify-write > operations use generic implementations that disable local interrupts. > > Implement RISC-V-specific this_cpu operations with preemption disabled > to keep accesses on the current CPU. Have you looked at some of the schemes (I think arm64 has the latest, but also s390) that do most per-cpu ops without disabling preemption. In particular they save the pre-emption check when pre-emption is enabled. Basically the code tells the scheduler which register contains the per-cpu data so that it can be 'magically' flipped during a context switch. David