Hi Marc, On Thu, Feb 17, 2022 at 1:12 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > On Thu, 17 Feb 2022 04:52:10 +0000, > Oliver Upton <oupton@xxxxxxxxxx> wrote: > > > > Hi Reiji, > > > > First off, thanks for looking into this! Seems like a very useful thing > > to test :-) > > > > On Wed, Feb 16, 2022 at 07:49:47PM -0800, Reiji Watanabe wrote: > > > Introduce a simple performance test of KVM_GET_ONE_REG/KVM_SET_ONE_REG > > > for registers that are returned by KVM_GET_REG_LIST. This is a pseudo > > > process of saving/restoring registers during live migration, and this > > > test quantifies the performance of the process. > > > > > > Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx> > > > --- > > > tools/testing/selftests/kvm/.gitignore | 1 + > > > tools/testing/selftests/kvm/Makefile | 1 + > > > .../selftests/kvm/aarch64/get_set_regs_perf.c | 456 ++++++++++++++++++ > > > > [...] > > > Would it make sense to test some opt-in capabilities that expose > > additional registers (PMU, SVE, etc.)? > > I think this is important. System registers are usually saved/restored Yes, I will fix the test to include registers for opt-in features when supported. > in groups, and due to the way we walk the sysreg array, timings are > unlikely to be uniform. Getting a grip on that could help restructure > the walking if required (either per-group arrays, or maybe a tree > structure). The biggest system register table that I know is sys_reg_descs[], and KVM_SET_ONE_REG/KVM_GET_ONE_REG/emulation code already uses binary search to find the target entry. So, the search itself isn't that bad. The difference between the min and the max latency of KVM_GET_ONE_REG for the registers is always around 200nsec on Ampere Altra machine as far as I checked. > Note that all of this could equally apply to the guest trapping (the > walk is the same). > > And yes, there are a lot of commonalities with get-reg-list, so > reusing some of the existing infrastructure would be a good thing. I will look into that. Thanks, Reiji _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
