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. > > 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? 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. > exports the latency info in a 100ms interval. > > To reduce overhead, latency info of children is propagated to parents > every 10ms. This means the parents's latency could lost 10ms info of its > children in 100ms. This should be ok, as we don't need precise latency > info. > > A micro benchmark running fio test against null_blk in a sixth level > cgroup doesn't show obvious regression. perf shows a little bit overhead > in blk_stat_add (~1%) and blkg_lookup (~1%), which is unavoidable right > now. > > With this patch, the io.stat will show: > 8:0 rbytes=7282688 wbytes=0 rios=83 wios=0 rlat_mean=2720 rlat_min=183 rlat_max=14880 wlat_mean=0 wlat_min=0 wlat_max=0 > The new fields will display read/write average/minimum/maximum latency > within 100ms. The latency is us. > Thanks Weiping
