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Wed, 5 Nov 2025 10:34:09 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D944C2004D; Wed, 5 Nov 2025 10:34:08 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CC23320043; Wed, 5 Nov 2025 10:34:06 +0000 (GMT) Received: from li-c9696b4c-3419-11b2-a85c-f9edc3bf8a84.in.ibm.com (unknown [9.109.198.245]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 5 Nov 2025 10:34:06 +0000 (GMT) From: Nilay Shroff To: linux-nvme@lists.infradead.org Cc: hare@suse.de, hch@lst.de, kbusch@kernel.org, sagi@grimberg.me, dwagner@suse.de, axboe@kernel.dk, kanie@linux.alibaba.com, gjoyce@ibm.com Subject: [RFC PATCHv5 7/7] nvme-multipath: add documentation for adaptive I/O policy Date: Wed, 5 Nov 2025 16:03:26 +0530 Message-ID: <20251105103347.86059-8-nilay@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251105103347.86059-1-nilay@linux.ibm.com> References: <20251105103347.86059-1-nilay@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTAxMDAyMSBTYWx0ZWRfX8pZh4RXrvleM 3LfwKAmaLYqGoWuVBkblgZelfj1xWBJ8jWRySU313DVlQkpMD0dPS4EoQmyAWGNXhRHHi827Ftj 4RvZGrFkUVgrfGE+c0BwLbhY7K13DHNmkLRFYDgkvljyCpq5RLI0vWU4RZ9NLYz68urA5GhLVAA iG3r7qRUihpTJhn/JjmpQL/9WQMh6JmQ6HJ49Kwvxqp/WdgubCBOWSTGLJ2Iw9mJM1shywv57yt jneSVAnCfCbVWTEuWXVDRj/a1WdZ2ukiFFt3erZVOD1nLeDQB0mMO/+lzqH77mdvzMZ6V8VAZsM +Onb8ZS13el3FXLFurMNHLClB5VkrtnncFb4WwfafFVO7n+w2QWBLVX2dNAYFEYDC5QQTrmpUWM lFsfFrVYaetjvD5rpKim82AMxuk4FQ== X-Proofpoint-GUID: AtbkHQH5XrgjejIvz5hu3L1cZQ-l6tQn X-Authority-Analysis: v=2.4 cv=OdCVzxTY c=1 sm=1 tr=0 ts=690b2824 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=SRrdq9N9AAAA:8 a=VnNF1IyMAAAA:8 a=NLV-vCcRgePVHmOrxzYA:9 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-ORIG-GUID: F1Leao-xclmQhwedqVAGAYk4ELYjP5pV X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-05_04,2025-11-03_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 spamscore=0 suspectscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511010021 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251105_093849_815123_07E10334 X-CRM114-Status: GOOD ( 12.58 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Update the nvme-multipath documentation to describe the adaptive I/O policy, its behavior, and when it is suitable for use. Suggested-by: Guixin Liu Signed-off-by: Nilay Shroff --- Documentation/admin-guide/nvme-multipath.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/admin-guide/nvme-multipath.rst b/Documentation/admin-guide/nvme-multipath.rst index 97ca1ccef459..7befaab01cf5 100644 --- a/Documentation/admin-guide/nvme-multipath.rst +++ b/Documentation/admin-guide/nvme-multipath.rst @@ -70,3 +70,22 @@ When to use the queue-depth policy: 1. High load with small I/Os: Effectively balances load across paths when the load is high, and I/O operations consist of small, relatively fixed-sized requests. + +Adaptive +-------- + +The adaptive policy manages I/O requests based on path latency. It periodically +calculates a weight for each path and distributes I/O accordingly. Paths with +higher latency receive lower weights, resulting in fewer I/O requests being sent +to them, while paths with lower latency handle a proportionally larger share of +the I/O load. + +When to use the adaptive policy +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +1. Homogeneous Path Performance: Utilizes all available paths efficiently when + their performance characteristics (e.g., latency, bandwidth) are similar. + +2. Heterogeneous Path Performance: Dynamically distributes I/O based on per-path + performance characteristics. Paths with lower latency receive a higher share + of I/O compared to those with higher latency. -- 2.51.0