On Wed, Oct 11, 2017 at 01:35:51AM +0800, weiping zhang wrote: > On Fri, Oct 06, 2017 at 05:56:01PM -0700, Shaohua Li wrote: > > From: Shaohua Li <shli@xxxxxx> > > > > Export the latency info to user. The latency is a good sign to indicate > > if IO is congested or not. User can use the info to make decisions like > > adjust cgroup settings. > Hi Shaohua, > How to check IO congested or not by latency ? Different SSD has > different latency especially when mixed sequence and random IO > operatons. There is no magic here, you should know the SSD characteristics first. The idea is observing the latency when the system isn't overcommited, for example, running the workload in a one-cgroup setup, then using the observed latency to guide configuration for multi-cgroup settings or check if IO is healthy in cgroups. > > > > Existing io.stat shows accumulated IO bytes and requests, but > > accumulated value for latency doesn't make much sense. This patch > How to understand "accumulated value for latency doesn't make much > sense" could you give an example? rbytes and wbytes in io.stat are accumulated value. If such value of latency isn't valuable. > I think iostat's r_await and w_await > are nearly equal to rlat_mean and wlat_mean if there is no too much > request starved. yes, pretty similar. io.stat is per-cgroup though Thanks, Shaohua
