On Tue, 27 Apr 2021 at 13:24, Odin Ugedal <odin@xxxxxxxxxx> wrote: > > Hi, > > > I wanted to say one v5.12-rcX version to make sure this is still a > > valid problem on latest version > > Ahh, I see. No problem. :) Thank you so much for taking the time to > look at this! > > > I confirm that I can see a ratio of 4ms vs 204ms running time with the > > patch below. > > (I assume you talk about the bash code for reproducing, not the actual > sched patch.) yes sorry > > > But when I look more deeply in my trace (I have > > instrumented the code), it seems that the 2 stress-ng don't belong to > > the same cgroup but remained in cg-1 and cg-2 which explains such > > running time difference. > > (mail reply number two to your previous mail might also help surface it) > > Not sure if I have stated it correctly, or if we are talking about the > same thing. It _is_ the intention that the two procs should not be in the > same cgroup. In the same way as people create "containers", each proc runs > in a separate cgroup in the example. The issue is not the balancing > between the procs > themselves, but rather cgroups/sched_entities inside the cgroup hierarchy. > (due to the fact that the vruntime of those sched_entities end up > being calculated with more load than they are supposed to). > > If you have any thought about the phrasing of the patch itself to make it > easier to understand, feel free to suggest. > > Given the last cgroup v1 script, I get this: > > - cat /proc/<stress-pid-1>/cgroup | grep cpu > 11:cpu,cpuacct:/slice/cg-1/sub > 3:cpuset:/slice > > - cat /proc/<stress-pid-2>/cgroup | grep cpu > 11:cpu,cpuacct:/slice/cg-2/sub > 3:cpuset:/slice > > > The cgroup hierarchy will then roughly be like this (using cgroup v2 terms, > becuase I find them easier to reason about): > > slice/ > cg-1/ > cpu.shares: 100 > sub/ > cpu.weight: 1 > cpuset.cpus: 1 > cgroup.procs - stress process 1 here > cg-2/ > cpu.weight: 100 > sub/ > cpu.weight: 10000 > cpuset.cpus: 1 > cgroup.procs - stress process 2 here > > This should result in 50/50 due to the fact that cg-1 and cg-2 both have a > weight of 100, and "live" inside the /slice cgroup. The inner weight should not > matter, since there is only one cgroup at that level. > > > So your script doesn't reproduce the bug you > > want to highlight. That being said, I can also see a diff between the > > contrib of the cpu0 in the tg_load. I'm going to look further > > There can definitely be some other issues involved, and I am pretty sure > you have way more knowledge about the scheduler than me... :) However, > I am pretty sure that it is in fact showing the issue I am talking about, > and applying the patch does indeed make it impossible to reproduce it > on my systems. Your script is correct. I was wrongly interpreting my trace. I have been able to reproduce your problem and your analysis is correct. Let me continue on the patch itself > > Odin
