Re: [libvirt] Suboptimal default cpu Cgroup

----- Original Message ----- > From: "Radim Krčmář" <rkrcmar(a)redhat.com&gt; > To: libvir-list(a)redhat.com > Cc: "Daniel P. Berrange" <berrange(a)redhat.com&gt;, "Andrew Theurer" <atheurer(a)redhat.com&gt; > Sent: Thursday, August 14, 2014 9:25:05 AM > Subject: Suboptimal default cpu Cgroup > > Hello, > > by default, libvirt with KVM creates a Cgroup hierarchy in 'cpu,cpuacct' > [1], with 'shares' set to 1024 on every level. This raises two points: > > 1) Every VM is given an equal amount of CPU time. [2] > ($CG/machine.slice/*/shares = 1024) > > Which means that smaller / less loaded guests are given an advantage. > > 2) All VMs combined are given 1024 shares. [3] > ($CG/machine.slice/shares) > > This is made even worse on RHEL7, by sched_autogroup_enabled = 0, so > every other process in the system is given the same amount of CPU as > all VMs combined. > > It does not seem to be possible to tune shares and get a good general > behavior, so the best solution I can see is to disable the cpu cgroup > and let users do it when needed. (Keeping all tasks in $CG/tasks.) Could we have each VM's shares be nr_vcpu * 1024, and the share for $CG/machine.slice be sum of all VM's share?