From: Coly Li <bosong.ly@xxxxxxxxxxxxxxx> Dm-latency patch set is an effort to measure hard disk I/O latency on top of device mapper layer. The original motivation of I/O latency measurement was to predict hard disk failure by machine learning method, I/O latency information was one of the inputs sent to machine learning model. This patch set was written in Aug~Sep 2013, I deployed it on many servers of Alibaba cloud infrastructure. After running for weeks, some interesting data about hard disk I/O latency was observed. In 2013, I gave a talk on OpenSuSE Conference about this topic (http://blog.coly.li/docs/osc13-coly.pdf). When generating time stamp for I/O request, clock source is a global unique resource which is protected by spin-locks. Dm-latency was tested on SAS/SATA hard disk and SATA SSD, it worked well as expected. Running dm-latency on PCI-e or NVMe SSD should work (I didn't test), but there will be spin-lock scalability issue, when accessing clock source for time stamping. Dm-latency is good for I/O latency measurement to hard disk based storage, no matter local or distributed storage via network. For PCI-e or NVMe SSD, I suggest people to look for device provided statistic information, if there is. The code is very simple, there is no resource allocation/destory, no spin_lock/spin_unlock. The patch set gets merged into Alibaba kernel more than 1 year, no bug reported in last 12 months. This patch set has 4 patches, - [PATCH 1/4] dm-latency: move struct mapped_device from dm.c to dm.h - [PATCH 2/4] dm-latency: add I/O latency measurement in device mapper - [PATCH 3/4] dm-latency: add sysfs interface - [PATCH 4/4] dm-latency: add reset function to dm-latency in sysfs interface All these patches are rebased on Linux 4.0-rc1. Today Laurence Oberman from Redhat sent me an email asking whether this patch set is upstream merged, because he is thinking of pulling this patch set into their kernel. I'd like to maintain this patch set, hope it could be merged. Thanks in advance. Coly Li -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
