Mark Rutland <mark.rutland@xxxxxxx> writes: > On Wed, Jan 18, 2017 at 02:51:31PM +0000, Punit Agrawal wrote: >> I should've clarified in my reply that I wasn't looking to support the >> third instance from Mark's examples above - "monitor all vCPUs on a >> pCPU". I think it'll be quite expensive to figure out which threads from >> a given pool are vCPUs. > > I'm not sure I follow why you would need to do that? > > In that case, we'd open a CPU-bound perf event for the pCPU, which would > get installed in the CPU context immediately. It would be present for > all tasks. > > Given it's present for all tasks, we don't need to figure out which > happen to have vCPUs. The !vCPU tasks simply shouldn't trigger events. > > Am I missing something? When enabling a CPU-bound event for pCPU, we'd have to enable trapping of TLB operations for the vCPUs running on pCPU. Have a look at Patch 7/9. Also, we'd have to enable/disable trapping when tasks are migrated between pCPUs. > >> For the other instances, we only need to find the vCPU for a given >> pid. Userspace will hand us a pid that needs to be checked against vCPUs >> to establish that it is a valid vCPU pid (here I was looking to use >> kvm_vcpu->pid and kvm->pid introduced in Patch 2). > > Thinking about this further, a pid is not a unique identifier for either > a vCPU or a VM. > > A single task (which has a single pid), could own multiple VMs, each > with multiple vCPUs. A thread pool (with several pids) could share those > arbitrarily. So we need VM and vCPU IDs which are distinct from pids or > tids. > > I see that struct kvm_vcpu has a vcpu_id (which from a glance appears to > be local to the kvm instance). It's not clear to me if a kvm instance > could be shared by multiple processes, or if we can get away with a > process-local ID. So far I've assumed that a VM pid is immutable. If that doesn't hold then we need to think of another mechanism to refer to a VM from userspace. > > Thanks, Mark. _______________________________________________ kvmarm >mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx >https://lists.cs.columbia.edu/mailman/listinfo/kvmarm -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
