Hello, This series attempts to solve some issues that arise from having some VCPUs be real-time while others aren't. We are trying to play media inside a VM on a desktop environment (Chromebooks), which requires us to have some tasks in the guest be serviced at real-time priority on the host so that the media can be played smoothly. To achieve this, we give a VCPU real-time priority on the host and use isolcpus= to ensure that only designated tasks are allowed to run on the RT VCPU. In order to avoid priority inversions (for example when the RT VCPU preempts a non-RT that's holding a lock that it wants to acquire), we dedicate a host core to the RT vcpu: Only the RT VCPU is allowed to run on that CPU, while all the other non-RT cores run on all the other host CPUs. This approach works on machines that have a large enough number of CPUs where it's possible to dedicate a whole CPU for this, but we also have machines that only have 2 CPUs and doing this on those is too costly. This patch series makes it possible to have a RT VCPU without having to dedicate a whole host core for it. It does this by making it so that non-RT VCPUs can't be preempted if they are in a critical section, which we approximate as having interrupts disabled or non-zero preempt_count. Once the VCPU is found to not be in a critical section anymore, it will give up the CPU. There measures to ensure that preemption isn't delayed too many times. (I realize that the hooks in the scheduler aren't very tasteful, but I couldn't figure out a better way. SVM support will be added when sending the patch for inclusion.) Feedback or alternatives are appreciated. Thanks, -- Suleiman Suleiman Souhlal (2): kvm,x86: Support heterogeneous RT VCPU configurations. kvm,x86: Report preempt_count to host. arch/x86/Kconfig | 11 +++++ arch/x86/include/asm/kvm_host.h | 7 +++ arch/x86/include/uapi/asm/kvm_para.h | 2 + arch/x86/kernel/kvm.c | 10 ++++ arch/x86/kvm/Kconfig | 13 ++++++ arch/x86/kvm/cpuid.c | 3 ++ arch/x86/kvm/vmx/vmx.c | 15 ++++++ arch/x86/kvm/x86.c | 70 +++++++++++++++++++++++++++- arch/x86/kvm/x86.h | 2 + include/linux/kvm_host.h | 4 ++ include/linux/preempt.h | 7 +++ kernel/sched/core.c | 30 ++++++++++++ virt/kvm/Kconfig | 3 ++ virt/kvm/kvm_main.c | 13 ++++++ 14 files changed, 189 insertions(+), 1 deletion(-) -- 2.32.0.432.gabb21c7263-goog
