Re: [PATCH v6 07/16] KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter

[Xu, Like]

On 2021/5/18 21:36, Peter Zijlstra wrote:
> On Tue, May 18, 2021 at 09:28:52PM +0800, Xu, Like wrote:
>
> > > How would pebs && !intr be possible?
> > I don't think it's possible.
> And yet you keep that 'intr||pebs' weirdness :/
>
> > > Also; wouldn't this be more legible
> > > when written like:
> > >
> > > 	perf_overflow_handler_t ovf = kvm_perf_overflow;
> > >
> > > 	...
> > >
> > > 	if (intr)
> > > 		ovf = kvm_perf_overflow_intr;
> > >
> > > 	...
> > >
> > > 	event = perf_event_create_kernel_counter(&attr, -1, current, ovf, pmc);
> > Please yell if you don't like this:
> >
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index 711294babb97..a607f5a1b9cd 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -122,6 +122,8 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc,
> > u32 type,
> >                  .config = config,
> >          };
> >          bool pebs = test_bit(pmc->idx, (unsigned long *)&pmu->pebs_enable);
> > +       perf_overflow_handler_t ovf = (intr || pebs) ?
> > +               kvm_perf_overflow_intr : kvm_perf_overflow;
> This, that's exactly the kind of code I wanted to get rid of. ?: has
> it's place I suppose, but you're creating dense ugly code for no reason.
>
> 	perf_overflow_handle_t ovf = kvm_perf_overflow;
>
> 	if (intr)
> 		ovf = kvm_perf_overflow_intr;
>
> Is so much easier to read. And if you really worry about that pebs
> thing; you can add:
>
> 	WARN_ON_ONCE(pebs && !intr);

Thanks!  Glad you could review my code.
As a new generation, we do appreciate your patient guidance on your taste 
in code.