Linux 4.1: Full DynTicks For KVM Guests To Become Possible

While full DynTicks support has been part of the mainline Linux kernel for quite a while, it's now become possible to use it with KVM guest virtual machines.

Full dynticks support for KVM guests will be possible with Linux 4.1 to support disabling the timer tick on the guest, per this NOHZ pull request by veteran kernel developer Ingo Molnar.

The patch finishing up this support explains, "The host kernel is not doing anything while the CPU is executing
a KVM guest VCPU, so it can be marked as being in an extended quiescent state, identical to that used when running user space code. The only exception to that rule is when the host handles an interrupt, which is already handled by the irq code, which calls rcu_irq_enter and rcu_irq_exit."

Those unfamiliar with the full dynticks support for the Linux kernel can see the kernel's NO_HZ documentation.