Hi Marc, On Sat, Jan 08, 2022 at 01:27:17PM +0000, Marc Zyngier wrote: > On Fri, 07 Jan 2022 12:10:05 +0000, > Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > > > Hi Marc, > > > > On Tue, Jan 04, 2022 at 02:39:59PM +0000, Marc Zyngier wrote: > > > On Mon, 15 Nov 2021 16:57:05 +0000, > > > Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > > > > > > > The KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_SET_PMU) VCPU ioctl is > > > > used to assign a physical PMU to the events that KVM creates when emulating > > > > the PMU for that VCPU. This is useful on heterogeneous systems, when there > > > > is more than one hardware PMU present. > > > > > > > > The assumption that is made in the implementation is that the user will > > > > pin the kvmtool process on a set of CPUs that share the same PMU. This > > > > allows kvmtool to set the same PMU for all VCPUs from the main thread, > > > > instead of in the individual VCPU threads. > > > > > > May I suggest a slightly different use model? Ideally, you'd be able > > > to run the vcpu threads on the CPUs matching the PMU affinity, and > > > leave all the other threads to roam on other CPUs. > > > > Right now, the only way for userspace to make kvmtool run on a particular > > set of CPUs in a heterogeneous configuration is to use taskset, which means > > the entire kvmtool process ends up being pinned on a subset of CPUs which > > have the same PMU. I would like to keep this approach, as it's simple and > > straightforward to implement in kvmtool, and it's easy to change in the > > future if there's an incentive to do so. > > > > It's also not clear to me how your suggestion would work. Add a command > > line argument to pin all the VCPUs to the specified cpumask? > > > > > > > > With your implementation, the whole of kvmtool gets stuck to a given > > > CPU type, which can be problematic. > > > > Do you have a specific use case in mind? Or is it more like a general > > concern regarding, for example, the virtio-blk-io or virtio-net-* threads > > competing with the VCPU threads if the VM is doing lots of I/O? > > Exactly that. The real requirement is that the vcpu thread affinities > are that of the PMU, but not that of any other thread. Maybe that's > just another parameter, independent of the PMU setup. Something like: > > lkvm run ... --vcpu-affinity $(< /sys/devices/armv8_pmuv3_0/cpus) > > for example. That should be easy (famous last words?) to implement as a separate patch on top of this series, I'll give that a go in the next iteration. Thanks for the suggestion. Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
