Hi We have already dm-statistics that counts various events - see Documentation/device-mapper/statistics.txt. It counts the nubmer of requests and the time spent servicing each request, thus you can calculate average latency from these values. Please look at dm-statistics to see if it fits your purpose. If you need additional information not provided by dm-statistics, it would be better to extend the statistics code rather than introduce new "latency" infrastructure. Mikulas On Thu, 26 Feb 2015, Coly Li wrote: > 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 > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
