On Wed, Jan 20, 2021 at 10:26:51AM +1000, Nicholas Piggin wrote:
> Excerpts from Aneesh Kumar K.V's message of January 19, 2021 7:45 pm:
> > Nicholas Piggin <npiggin@xxxxxxxxx> writes:
> >
> >> As explained in the comment, there is no need to flush TLBs on all
> >> threads in a core when a vcpu moves between threads in the same core.
> >>
> >> Thread migrations can be a significant proportion of vcpu migrations,
> >> so this can help reduce the TLB flushing and IPI traffic.
> >>
> >> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> >> ---
> >> I believe we can do this and have the TLB coherency correct as per
> >> the architecture, but would appreciate someone else verifying my
> >> thinking.
> >>
> >> Thanks,
> >> Nick
> >>
> >> arch/powerpc/kvm/book3s_hv.c | 28 ++++++++++++++++++++++++++--
> >> 1 file changed, 26 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> >> index 752daf43f780..53d0cbfe5933 100644
> >> --- a/arch/powerpc/kvm/book3s_hv.c
> >> +++ b/arch/powerpc/kvm/book3s_hv.c
> >> @@ -2584,7 +2584,7 @@ static void kvmppc_release_hwthread(int cpu)
> >> tpaca->kvm_hstate.kvm_split_mode = NULL;
> >> }
> >>
> >> -static void radix_flush_cpu(struct kvm *kvm, int cpu, struct kvm_vcpu *vcpu)
> >> +static void radix_flush_cpu(struct kvm *kvm, int cpu, bool core, struct kvm_vcpu *vcpu)
> >> {
> >
> > Can we rename 'core' to something like 'core_sched' or 'within_core'
> >
> >> struct kvm_nested_guest *nested = vcpu->arch.nested;
> >> cpumask_t *cpu_in_guest;
> >> @@ -2599,6 +2599,14 @@ static void radix_flush_cpu(struct kvm *kvm, int cpu, struct kvm_vcpu *vcpu)
> >> cpu_in_guest = &kvm->arch.cpu_in_guest;
> >> }
> >>
> >
> > and do
> > if (core_sched) {
>
> This function is called to flush guest TLBs on this cpu / all threads on
> this cpu core. I don't think it helps to bring any "why" logic into it
> because the caller has already dealt with that.
I agree with Aneesh that the name "core" doesn't really help the
reader to know what the parameter means. Either it needs a comment or
a more descriptive name.
Paul.
