On 11/10/21 06:13, Felix Moessbauer wrote:
Hi Weiman,v8: - Reorganize the patch series and rationalize the features and constraints of a partition. - Update patch descriptions and documentation accordingly. v7: - Simplify the documentation patch (patch 5) as suggested by Tejun. - Fix a typo in patch 2 and improper commit log in patch 3. v6: - Remove duplicated tmpmask from update_prstate() which should fix the frame size too large problem reported by kernel test robot. This patchset makes four enhancements to the cpuset v2 code. Patch 1: Enable partition with no task to have empty cpuset.cpus.effective. Patch 2: Refining the features and constraints of a cpuset partition clarifying what changes are allowed. Patch 3: Add a new partition state "isolated" to create a partition root without load balancing. This is for handling intermitten workloads that have a strict low latency requirement.I just tested this patch-series and can confirm that it works on 5.15.0-rc7-rt15 (PREEMT_RT). However, I was not able to see any latency improvements when using cpuset.cpus.partition=isolated. The test was performed with jitterdebugger on CPUs 1-3 and the following cmdline: rcu_nocbs=1-4 nohz_full=1-4 irqaffinity=0,5-6,11 intel_pstate=disable On the other cpus, stress-ng was executed to generate load. Just some more general notes: Even with this new "isolated" type, it is still very tricky to get a similar behavior as with isolcpus (as long as I don't miss something here): Consider an RT application that consists of a non-rt thread that should be floating and a rt-thread that should be placed in the isolated domain. This requires cgroup.type=threaded on both cgroups and changes to the application (threads have to be born in non-rt group and moved to rt-group). Theoretically, this could be done externally, but in case the application sets the affinity mask manually, you run into a timing issue (setting affinities to CPUs outside the current cpuset.cpus results in EINVAL).
I believe the "isolated" type will have more benefit on non PREEMPT_RT kernel. Anyway, having the "isolated" type is just the first step. It should be equivalent to "isolcpus=domain". There are other patches floating that attempt to move some of the isolcpus=nohz features into cpuset as well. It is not there yet, but we should be able to have better dynamic cpu isolation down the road.
Cheers, Longman
