On Thu, Feb 26, 2015 at 11:49:28AM -0500, Mikulas Patocka wrote: > 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. Right: average service time (as reported by iostat etc.) is easily derived from the existing stats. Does the separate latency accounting buy anything additional? > 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. Agreed; I'm working on userspace support for dm-statistics at the moment and if there is a need for these additional measurements I would greatly prefer to consume them as additional fields in the existing dm-stats counter set. This also has the advantage of benefiting from the existing step and area support allowing a device to be subdivided into discrete stats regions. Regards, Bryn. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
