From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-72.mta0.migadu.com [91.218.175.72]) (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 A7E3344AB91 for ; Wed, 30 Sep 2026 07:52:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.72 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790754756; cv=none; b=F/+urz7Nf+9cjQtuJqYIE0oXq5+DQ444z1P7JCqzB0rihlv9fHF/ycx65ouS618WzGBIz2TEinRSoEkf6CAgiZYKMZfvhOOeRmL30P4Yr60VOFO59UzHoxPjxBbOJVBQSez4ZV3DMR62Ks/LfnpsGoze1EzIDASxrKl71sX5u6E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790754756; c=relaxed/simple; bh=8ma5wy0oJIj/chbeeAhuh0ZtFGfNhOnQTVLc6I5RlKQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mbodxr+5RTPqO2WwZ0W+pBew3BbfrFYgxFnMAzvylPUk87SwZWQaqZ80xSPmf32PXjlpebd5ie19sv0Sm/J3/mm5n5I5gPDi1fVD7x71p4YguvOH5RCfnIlmDahi2okUdOjuZS76j0inmq8jWc37qocmUQsW+6xDB+W+EJDkzqo= 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=hoyIe2tV; arc=none smtp.client-ip=91.218.175.72 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="hoyIe2tV" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=8ma5wy0oJIj/chbeeAhuh0ZtFGfNhOnQTVLc6I5RlKQ=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790754752; v=1; x=1791359552; b=hoyIe2tVu7LbrNdOK4BCoPaXkPloBQPEyssSc7kF0Js8c9v8xA2QemWicEDl2OqDyVZGiYzZ RWR6Lmt3LpI/XrLGa4RsriPvM5M9TGjN5Ne1HMCH4FxBo0OL4w7Fx7tLYDjzqCMhCY7QQM/1lB1 0t2AyW2lyN5zFhmrPQ54bIlI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 7b477e88c5b0e9d9; Wed, 30 Sep 2026 07:52:32 +0000 X-Mizu-Trace-ID: 7b477e88c5b0e9d9 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 v8 4/4] docs: cgroup-v2: document the iocost BPF cost model attachment Date: Wed, 30 Sep 2026 15:51:54 +0800 Message-ID: <20260930075154.189958-5-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260930075154.189958-1-cui.tao@linux.dev> References: <20260930075154.189958-1-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. Signed-off-by: Tao Cui --- Documentation/admin-guide/cgroup-v2.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 7fe950425216..5e780bdcf324 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2117,8 +2117,27 @@ 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 attached to a device by loading an "iocost_model_ops" + struct_ops with 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. "ctrl" 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