Alex, On Mon, 13 Dec 2021 15:23:05 +0000, Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > (CC'ing Peter Maydell in case this might be of interest to qemu) > > The series can be found on a branch at [1], and the kvmtool support at [2]. > The kvmtool patches are also on the mailing list [3] and haven't changed > since v1. > > Detailed explanation of the issue and symptoms that the patches attempt to > correct can be found in the cover letter for v1 [4]. > > A summary of the problem is that on heterogeneous systems KVM will always > use the same PMU for creating the VCPU events for *all* VCPUs regardless of > the physical CPU on which the VCPU is running, leading to events suddenly > stopping and resuming in the guest as the VCPU thread gets migrated across > different CPUs. > > This series proposes to fix this behaviour by allowing the user to specify > which physical PMU is used when creating the VCPU events needed for guest > PMU emulation. When the PMU is set, KVM will refuse to the VCPU on a > physical which is not part of the supported CPUs for the specified PMU. The > restriction is that all VCPUs must use the same PMU to avoid emulating an > asymmetric platform. > > The default behaviour stays the same - without userspace setting the PMU, > events will stop counting if the VCPU is scheduled on the wrong CPU. > > Tested with a hacked version of kvmtool that does the PMU initialization > from the VCPU thread as opposed to from the main thread. Tested on > rockpro64 by testing what happens when all VCPUs having the same PMU, one > random VCPU having a different PMU than the other VCPUs and one random VCPU > not having the PMU set (each test was run 1,000 times on the little cores > and 1,000 times on the big cores). > > Also tested on an Altra by testing all VCPUs having the same PMU, all VCPUs > not having a PMU set, and one random VCPU not having the PMU set; the VM > had 64 threads in each of the tests and each test was run 10,000 times. Came back to this series, and found more problems. On top of the remarks I had earlier (the per-CPU data structures that really should per VM, the disappearing attribute size), what happens when event filters are already registered and that you set a specific PMU? I took the matter in my own hands (the joy of being in quarantine) and wrote whatever fixes I thought were necessary[1]. Please have a look. M. [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/pmu-bl -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
