From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.85 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793712434; b=0EZQ5QVHxfc4AGTUsfgVX2YHNyxOF3ZFtHUceYhYFOWPI1HHBmgUXdyJ0jbEFsrx3cX2 Y2T8196+Dz+fvNpxCTSSnLJ8ovGFM+CtWuL58pMJdZq/h7Dz2jj9/pO63cH2d8ebNXF2L inBwpjSFzBCy/Z68zgMqaSrbtz/WmwPKM4TEQ97b7uUG//Uak8om/8Tel1uBsRnIIGGxE FKq/F45vbc8vfwp+4o2Bwro2rUSMCKPeNE/j5yaKUDpRJA2xnKT8nR+ZOEVvLDkNE+mI7 gIkKTrNg8omtyaDSyX9gdFq96PZEeixB3+u46hxKL4PaN7IipM0OGU2pLSTM9KAIjmA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793712434; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=9VAhO8KBM9mOdifI8nmOoX/2TqgeYxG3nBGm5R3+hSk=; b=kRZxDSlMIuvgtCQAQNdR+pUCih2ADNOJ5/flIpYbvTM5ugtUNsCEd9L6njShD0CqABIk dOPPpr6FO6P82ub8aecYkDJNOoAffOLFoM2DTHvi8st1RG0LwGVfd4LCeiacjPTI61AZr y08tWmbCUyfFoRYpXKMp7TpQzIY58EVl4JtL5EQciCWoMXsLRDYwghVE4U33V0TNn60Ha j8GQkx+ci7Q00Bvf/40FWf5vqIuLvf7vc6wuOEPBVfJuaKXDVNJpF8qIEIPSyxocip1eG Fs8ka2vRr0Dwio9R7kC9+5IBMcozorEM/NhNyh4/3HkLdN5tEVHTD46vM1I1x56O5uw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Ft9Xbzm+; arc=none smtp.remote-ip=95.215.58.85 Received: from mta1.migadu.com (out-85.mta1.migadu.com [95.215.58.85]) (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 2409E606EE92 for ; Tue, 3 Nov 2026 13:27:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2409E606EE92 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, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Ft9Xbzm+ X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=dZMvqS4c+48JMUQ62nOXGEohEi1C+eqSvF1H1cvPGHA=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793712432; v=1; x=1794317232; b=Ft9Xbzm+hW0qsnAN47NDcXZySQXr2QHs7P80TV6VfaOgfM3Eqhj/enxkM44uB2uoF/M8ZKA5 /UYXMhvs+9RJW90axiwz8e36Yus1sqoByZW6lQjXcuBk1Fal7D3gLVrzcTr0N7qqOaKSsntw5ZU xKgkAUdfUfPqfkmX727/CA0o= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id fb2cfe47defad250; Tue, 03 Nov 2026 13:27:11 +0000 X-Mizu-Trace-ID: fb2cfe47defad250 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: tj@kernel.org, josef@toxicopanda.com, axboe@kernel.dk, alexei.starovoitov@gmail.com 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 Subject: [RFC PATCH v12 4/4] docs: cgroup-v2: document the iocost BPF cost model attachment Date: Tue, 3 Nov 2026 21:26:13 +0800 Message-ID: <20261103132613.1952975-5-cui.tao@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261103132613.1952975-1-cui.tao@linux.dev> References: <20261103132613.1952975-1-cui.tao@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui 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), the builtin model coming back on detach, and ctrl writes never selecting a model. Suggested-by: Tejun Heo Signed-off-by: Tao Cui --- Documentation/admin-guide/cgroup-v2.rst | 45 ++++++++++++++++++++----- 1 file changed, 37 insertions(+), 8 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 9e3c67b02ae2..0965645b1286 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2056,8 +2056,9 @@ IO Interface Files currently implements "io.weight" proportional control. Lines are keyed by $MAJ:$MIN device numbers and not ordered. The line for a given device is populated on the first write for - the device on "io.cost.qos" or "io.cost.model". The following - nested keys are defined. + the device on "io.cost.qos" or "io.cost.model", or when a BPF + cost model is attached to it. The following nested keys are + defined. ====== ===================================== enable Weight-based control enable @@ -2111,13 +2112,40 @@ IO Interface Files implements "io.weight" proportional control. Lines are keyed by $MAJ:$MIN device numbers and not ordered. The line for a given device is populated on the first write for the device on - "io.cost.qos" or "io.cost.model". The following nested keys - are defined. + "io.cost.qos" or "io.cost.model", or when a BPF cost model is + attached to it. The following nested keys are defined. - ===== ================================ + ===== ========================================== ctrl "auto" or "user" - model The cost model in use - "linear" - ===== ================================ + model The cost model in use - "linear" or "bpf" + ===== ========================================== + + When BPF cost model support is available, 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 as encoded by makedev(3) in its "dev" member (a + partition's major:minor is rejected). Attaching creates the + controller if needed, like + an io.cost.model write does, switches the device's pricing to + the model and populates the device's line in this file and in + "io.cost.qos" if it did not exist yet. Attaching fails with + -EBUSY if the device already has a model attached. The + attached model prices IOs only while the controller is + enabled through "io.cost.qos"; attaching does not enable it. + IOs issued directly by the root cgroup bypass the model. + + 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. + + 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 take effect + again when switched back. When "ctrl" is "auto", the kernel may change all parameters dynamically. When "ctrl" is set to "user" or any other @@ -2125,7 +2153,8 @@ IO Interface Files automatic changes are disabled. When "model" is "linear", the following model parameters are - defined. + defined. They remain readable and writable while "model" is + "bpf". ============= ======================================== [r|w]bps The maximum sequential IO throughput -- 2.53.0