On Mon, Dec 03, 2018 at 04:58:43PM +0000, Will Deacon wrote:
> On Mon, Dec 03, 2018 at 03:05:52PM +0000, Andrew Murray wrote:
> > On Mon, Dec 03, 2018 at 02:31:14PM +0000, Will Deacon wrote:
> > > On Thu, Nov 22, 2018 at 11:25:48AM +0000, Andrew Murray wrote:
> > > > In order to effeciently enable/disable guest/host only perf counters
> > > > at guest entry/exit we add bitfields to kvm_cpu_context for guest and
> > > > host only events as well as accessors for updating them.
> > > >
> > > > Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
> > > > ---
> > > > arch/arm64/include/asm/kvm_host.h | 20 ++++++++++++++++++++
> > > > 1 file changed, 20 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > > > index 1550192..4a828eb 100644
> > > > --- a/arch/arm64/include/asm/kvm_host.h
> > > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > > @@ -203,6 +203,8 @@ struct kvm_cpu_context {
> > > > };
> > > >
> > > > struct kvm_vcpu *__hyp_running_vcpu;
> > > > + u32 events_host_only;
> > > > + u32 events_guest_only;
> > > > };
> > > >
> > > > typedef struct kvm_cpu_context kvm_cpu_context_t;
> > > > @@ -472,6 +474,24 @@ static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
> > > > {
> > > > return kvm_arch_vcpu_run_map_fp(vcpu);
> > > > }
> > > > +static inline void kvm_clr_set_host_pmu_events(u32 clr, u32 set)
> > > > +{
> > > > + kvm_cpu_context_t *ctx = this_cpu_ptr(&kvm_host_cpu_state);
> > > > +
> > > > + ctx->events_host_only &= ~clr;
> > > > + ctx->events_host_only |= set;
> > > > +}
> > >
> > > Do you actually need this clr/set function, or can you just use the
> > > facilities provided by bitfield.h at the callsites?
> >
> > This modifies events_{host|guest}_only which is conditionally defined
> > (CONFIG_KVM) yet used by arch/arm64/kernel/perf_events which is also
> > conditionally defined (CONFIG_HW_PERF_EVENTS). By moving this away
> > from the callsite we avoid a load of horrible #ifdef's and allow this
> > function to become a nop when KVM isn't enabled.
> >
> > Is there value in updating this function to use set_bit/clear_bit
> > functions in bitops/atomic.h ?
>
> You don't need the atomicity, so you'd be looking at the '__' variants
> instead. My main concern is that we're introducing a clr_set_* API which
> only ever clears or sets, so I think it's needlessly complicated. If you
> need two separate macros that are just #defined to __set_bit/__clear_bit
> or expand to nothing then that could work too.
Though it would be 4 macros - a set and clear for both events_host and
events_guest. Though with the proposed changes in the other patch, this
could end up being 3 macros seeing as we'd always clear both events_host
and events_guest at the same time.
Thanks,
Andrew Murray
>
> Will
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