From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-92.mta1.migadu.com [95.215.58.92]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D04E636F434 for ; Sat, 3 Oct 2026 01:31:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.92 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790991083; cv=none; b=trCLUW+gZlp+e01n4QnLeKyQRyYr1862FgXHHBeB0c4YEx/mTzkmtXzYeL1a0pAACyQhjcm5PpKYCuh+Ja/uzv6lTdjUprNRBqhwcMiweSrgX4QMU2nTItuRcwtqmI4isgVxLsbSaMQB0qybph1114tVrbUuxcLgBROni9DrIEI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790991083; c=relaxed/simple; bh=VrUjaFpfqhbBta7NxOheeA+88Rj1Be533vYMgr2BzzY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=if094ZVxqArCZZvoqQt3/DTp4iwtnM2FJdAHofc4uu78V+FPaNIgZZJLuTClto7N7CmjT2CdNl+f5dIT1r190Djc7Dsse40s0JavpbviJLLvTR1j9ixI0dWEopkycvQG8LDcGGyiQu8arW3zrfjSOPh0hwP0APRkxTOPoMfQipM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=u1d9uVxc; arc=none smtp.client-ip=95.215.58.92 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="u1d9uVxc" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=VrUjaFpfqhbBta7NxOheeA+88Rj1Be533vYMgr2BzzY=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790991079; v=1; x=1791595879; b=u1d9uVxcC7a/c+SWtsy3W63ylACVacB5mNkYIEnmZaMc0oWfpiSIMxnW4pQi+fzi5+tm9x/U d74svHx31UNJnLh08R+5XjZtumOk2znDI3b9EWiXGAj1/lgxOdrwcmK6ySRpGZb+Iz/oQqTMS41 N4Rc6Qg8ery6wYjbSFyP+22E= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id ed5ea994910a12e4; Sat, 03 Oct 2026 01:31:19 +0000 X-Mizu-Trace-ID: ed5ea994910a12e4 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: tj@kernel.org, josef@toxicopanda.com, axboe@kernel.dk Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, andrii@kernel.org, eddyz87@gmail.com, ast@kernel.org, daniel@iogearbox.net, linux-kselftest@vger.kernel.org, cui.tao@linux.dev, cuitao@kylinos.cn, ameryhung@gmail.com, alexei.starovoitov@gmail.com Subject: [RFC PATCH v9 4/4] docs: cgroup-v2: document the iocost BPF cost model attachment Date: Sat, 3 Oct 2026 09:30:33 +0800 Message-ID: <20261003013033.149288-5-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261003013033.149288-1-cui.tao@linux.dev> References: <20261003013033.149288-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Document the BPF cost model attachment in the io.cost.model section of the cgroup v2 documentation: attaching an iocost_model_ops struct_ops to a device by its major:minor, the model=bpf readback while attached (ctrl keeps describing the coefficients), that detaching restores the builtin model, and that ctrl= writes never select a model. Suggested-by: Tejun Heo Signed-off-by: Tao Cui --- Documentation/admin-guide/cgroup-v2.rst | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 7fe950425216c..07da465bb4ef0 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2117,8 +2117,31 @@ IO Interface Files ===== ================================ ctrl "auto" or "user" model The cost model in use - "linear" + or "bpf" while the BPF model + is in use ===== ================================ + When CONFIG_BLK_CGROUP_IOCOST_BPF is enabled, a BPF cost model + can be bound to a device by attaching an "iocost_model_ops" + struct_ops carrying the whole disk's major:minor in its "dev" + member (a partition's major:minor is rejected). Attaching creates + the + controller if needed, like an io.cost.model write does, and + switches the device's pricing to the model; enabling and + disabling the controller stays with io.cost.qos. While a model + is attached, "model" selects between it and the builtin model: + "model=bpf" switches to the attached model and "model=linear" + switches back to the builtin model, and neither detaches the + struct_ops; only detaching removes the model, after which + "model=bpf" fails and the device prices with the builtin model + again. Device removal ejects the attached model as well, while + the struct_ops link remains until userspace destroys it. "ctrl" + accepts only "auto" and "user" and never + selects a model; it keeps describing the builtin coefficients, + which are kept while the BPF model is in use and take effect + again when switched back, and the automatic profile stepping + does not switch profiles while the BPF model is in use. + When "ctrl" is "auto", the kernel may change all parameters dynamically. When "ctrl" is set to "user" or any other parameters are written to, "ctrl" become "user" and the -- 2.43.0