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Wed, 20 May 2026 18:22:03 +0000 (GMT) Received: from li-a84c74cc-2b13-11b2-a85c-acdd023f0674.ibm.com.com (unknown [9.61.40.237]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 20 May 2026 18:22:01 +0000 (GMT) From: Nilay Shroff To: linux-nvme@lists.infradead.org Cc: hare@suse.de, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, dwagner@suse.de, kanie@linux.alibaba.com, jmeneghi@redhat.com, randyj@purestorage.com, martin.petersen@oracle.com, john.g.garry@oracle.com, gjoyce@linux.ibm.com Subject: [PATCHv6 8/8] nvme-multipath: add documentation for latency I/O policy Date: Wed, 20 May 2026 23:51:04 +0530 Message-ID: <20260520182112.863076-9-nilay@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260520182112.863076-1-nilay@linux.ibm.com> References: <20260520182112.863076-1-nilay@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=ffCdDUQF c=1 sm=1 tr=0 ts=6a0dfbd5 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=SRrdq9N9AAAA:8 a=VnNF1IyMAAAA:8 a=5c6VxMoH-_C0Ghh2t7EA:9 X-Proofpoint-ORIG-GUID: wVqHx_Rn61dwoqZ02Dao0urWbGZqEFZs X-Proofpoint-GUID: k_0pqB2hKMEmxqH24NcO6OTZziIk_o8X X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTIwMDE3NyBTYWx0ZWRfX3SwFB4xzEPJY HCZgDVPnzsW1BnySrqJzE4VeDGOlLB55eH4wWQ4vwuqAARoZ0vrubSbqdDRhvPrJ/+nmyN+KowD JtnYxrNeOWhNvlVjnf7XU2tNorOivR2cvuQvOB09ICg+H1U6s+3ikVFXAFn12ZZHBGuBT4jt3lr 9xJLeo8oBn6cIdWnWcEc3e/3PtB7Eh+TgdMCmfUogmuY7DC6Mwfqi1bOxcpM99icsA3OLfUGPNV OOgLEJAWmLYBsNDJ1kpTCdyR8fTILbH1QPPsUe1U4QIOf+2Y45G0TZx7Kth99WtjbiyEUWhDLXs vgcXOzEmTiGkx3UWNPWKuJRwMps3Y9EF/2R6PXRAqh270ZQgaecpEmPFyfQf49KoGPL4bF3gAjl yh/baWec7GgAWrZARbcPxrufEby2HXiY3obVqxSGp8EcJpQKkCCtVZsBoSpB58MDB1q8U/2eGEB jvevoG4NK+h60XH8lQw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-20_03,2026-05-18_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 phishscore=0 suspectscore=0 adultscore=0 clxscore=1015 impostorscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605200177 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260520_192222_786021_50896B8F X-CRM114-Status: GOOD ( 12.23 ) 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 latency 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..41a8054638ff 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. + +Latency +-------- + +The latency 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 latency 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. -- 2.53.0