On Sat, Sep 18, 2010 at 02:38:15PM -1000, Zachary Amsden wrote: > Negate the effects of AN TYM spell while kvm thread is preempted by tracking > conversion factor to the highest TSC rate and catching the TSC up when it has > fallen behind the kernel view of time. Note that once triggered, we don't > turn off catchup mode. > > A slightly more clever version of this is possible, which only does catchup > when TSC rate drops, and which specifically targets only CPUs with broken > TSC, but since these all are considered unstable_tsc(), this patch covers > all necessary cases. > > Signed-off-by: Zachary Amsden <[email protected]> > --- > arch/x86/include/asm/kvm_host.h | 6 +++ > arch/x86/kvm/x86.c | 87 +++++++++++++++++++++++++++++--------- > 2 files changed, 72 insertions(+), 21 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 8c5779d..e209078 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -384,6 +384,9 @@ struct kvm_vcpu_arch { > u64 last_host_tsc; > u64 last_guest_tsc; > u64 last_kernel_ns; > + u64 last_tsc_nsec; > + u64 last_tsc_write; > + bool tsc_catchup; > > bool nmi_pending; > bool nmi_injected; > @@ -444,6 +447,9 @@ struct kvm_arch { > u64 last_tsc_nsec; > u64 last_tsc_offset; > u64 last_tsc_write; > + u32 virtual_tsc_khz; > + u32 virtual_tsc_mult; > + s8 virtual_tsc_shift; > > struct kvm_xen_hvm_config xen_hvm_config; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 09f468a..9152156 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -962,6 +962,7 @@ static inline u64 get_kernel_ns(void) > } > > static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz); > +unsigned long max_tsc_khz; > > static inline int kvm_tsc_changes_freq(void) > { > @@ -985,6 +986,24 @@ static inline u64 nsec_to_cycles(u64 nsec) > return ret; > } > > +static void kvm_arch_set_tsc_khz(struct kvm *kvm, u32 this_tsc_khz) > +{ > + /* Compute a scale to convert nanoseconds in TSC cycles */ > + kvm_get_time_scale(this_tsc_khz, NSEC_PER_SEC / 1000, > + &kvm->arch.virtual_tsc_shift, > + &kvm->arch.virtual_tsc_mult); > + kvm->arch.virtual_tsc_khz = this_tsc_khz; > +} > + > +static u64 compute_guest_tsc(struct kvm_vcpu *vcpu, s64 kernel_ns) > +{ > + u64 tsc = pvclock_scale_delta(kernel_ns-vcpu->arch.last_tsc_nsec, > + vcpu->kvm->arch.virtual_tsc_mult, > + vcpu->kvm->arch.virtual_tsc_shift); > + tsc += vcpu->arch.last_tsc_write; > + return tsc; > +} > + > void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) > { > struct kvm *kvm = vcpu->kvm; > @@ -1029,6 +1048,8 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) > > /* Reset of TSC must disable overshoot protection below */ > vcpu->arch.hv_clock.tsc_timestamp = 0; > + vcpu->arch.last_tsc_write = data; > + vcpu->arch.last_tsc_nsec = ns; > } > EXPORT_SYMBOL_GPL(kvm_write_tsc); > > @@ -1041,22 +1062,42 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > s64 kernel_ns, max_kernel_ns; > u64 tsc_timestamp; > > - if ((!vcpu->time_page)) > - return 0; > - > /* Keep irq disabled to prevent changes to the clock */ > local_irq_save(flags); > kvm_get_msr(v, MSR_IA32_TSC, &tsc_timestamp); > kernel_ns = get_kernel_ns(); > this_tsc_khz = __get_cpu_var(cpu_tsc_khz); > - local_irq_restore(flags); > > if (unlikely(this_tsc_khz == 0)) { > + local_irq_restore(flags); > kvm_make_request(KVM_REQ_CLOCK_UPDATE, v); > return 1; > } > > /* > + * We may have to catch up the TSC to match elapsed wall clock > + * time for two reasons, even if kvmclock is used. > + * 1) CPU could have been running below the maximum TSC rate
kvmclock handles frequency changes? > + * 2) Broken TSC compensation resets the base at each VCPU > + * entry to avoid unknown leaps of TSC even when running > + * again on the same CPU. This may cause apparent elapsed > + * time to disappear, and the guest to stand still or run > + * very slowly. I don't get this. Please explain. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
