Hi all, On Tue, 25 Apr 2017 11:13:03 +0100 Juri Lelli <juri.lelli@xxxxxxx> wrote: [...] > > > Currently, KVM do the CPU resource reservation by the cgroup > > > mechanism which can't do entire accurate separation because the > > > capacity of the Linux scheduler. Take the public cloud as an > > > example, some customers rent one vm with 8 CPUs paid by enough > > > money, they want to get enough response speed on CPU scheduling. > > > So we (the cloud platform providers ) reserve 1GHz CPU resources > > > by cgroup for those VM's vcpu/pcpu. > > > > > > But the actual effects can't meet those requirements because the > > > cgroup is limiting share usage of other processes in order to > > > attach the reservation proportion, but the scheduler can't assure > > > that. This mechanism is different with Xen, We can directly > > > change the CPU weight on Xen hypervisor so that we can get entire > > > accurate control on CPU resources based on accurate capacity > > > (upper limit), share (weight) and reservation. > > > > > > So my question is do we have a good method to do CPU reservation > > > in KVM? > > > > > > Thanks, > > > -Gonglei > > Not entirely sure what your particular requirements are Gonglei, but > you might be interested to know that there has been research work > [1,2,3, just to name a few] that used a mainline real-time scheduling > policy (SCHED_DEADLINE) to provide Qos support to virtual machines > (KVM). > > I won't enter in too much detail, but the basic idea is to use > reservation based scheduling mechanisms to enforce temporal isolation > and guaranteed CPU bandwidth to VM's vcpu(s). Since I've been CC-ed, I add some details to what Juri wrote: if the guest workload is mostly CPU intensive, just scheduling the vCPU threads with SCHED_DEADLINE allows deterministic CPU allocation. I recently showed some experiments about this to some students: if some periodic real-time tasks are executed in the guest and KVM's vCPU threads are scheduled with SCHED_DEADLINE, then the number of missed deadlines measured in the guest matches with the number of missed deadlines expected from theoretical analysis (using real-time hierarchical scheduling analysis). [I can provide more details if needed: here is a quick and incomplete summary I wrote for the students: http://retis.sssup.it/~luca/CBSD/h-sched_experiments.txt up to item 4 it is just theoretical schedulability analysis; the interesting parts start from item 5] I think this shows that (for CPU-intensive workloads) it is possible to deterministically control the QoS of a KVM-based VM by using SCHED_DEADLINE. If your guest workload includes more I/O, then you have to schedule more threads with SCHED_DEADLINE (for example, I have some experiments with a lot of network traffic in the guest; I used vhost-net and I've been able to control the network throughput by scheduling the vhost-net kernel thread with SCHED_DEADLINE and changing the runtime and period associated to thread). Luca > > I'm Cc-ing Tommaso, Luca and Carlo, whom can provide more information > as needed. > > Best, > > - Juri > > [1] - http://retis.sssup.it/~nino/publication/rtlws14sdnnfs.pdf > [2] - http://retis.sssup.it/~tommaso/publications/VHPC-2010.pdf > [3] - http://retis.sssup.it/~tommaso/publications/RTSOAA-2009-RTV.pdf > > Skimming through Tommaso and Luca publications might be interesting as > well. I'm pretty sure I missed the most importants papers. :) > http://retis.sssup.it/~tommaso/eng/publications.html > https://scholar.google.co.uk/citations?user=C3a6glEAAAAJ&hl=en
