On Thu, Jun 13, 2019 at 05:50:43PM +0100, Suzuki K Poulose wrote:
>
>
> On 13/06/2019 10:39, Andrew Murray wrote:
> > On Thu, Jun 13, 2019 at 08:30:51AM +0100, Julien Thierry wrote:
> > > Hi Andrew,
> > >
> > > On 12/06/2019 20:04, Andrew Murray wrote:
> > > > We currently use pmc->bitmask to determine the width of the pmc - however
> > > > it's superfluous as the pmc index already describes if the pmc is a cycle
> > > > counter or event counter. The architecture clearly describes the widths of
> > > > these counters.
> > > >
> > > > Let's remove the bitmask to simplify the code.
> > > >
> > > > Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
> > > > ---
> > > > include/kvm/arm_pmu.h | 1 -
> > > > virt/kvm/arm/pmu.c | 19 +++++++++----------
> > > > 2 files changed, 9 insertions(+), 11 deletions(-)
> > > >
> > > > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> > > > index b73f31baca52..2f0e28dc5a9e 100644
> > > > --- a/include/kvm/arm_pmu.h
> > > > +++ b/include/kvm/arm_pmu.h
> > > > @@ -28,7 +28,6 @@
> > > > struct kvm_pmc {
> > > > u8 idx; /* index into the pmu->pmc array */
> > > > struct perf_event *perf_event;
> > > > - u64 bitmask;
> > > > };
> > > > struct kvm_pmu {
> > > > diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> > > > index ae1e886d4a1a..88ce24ae0b45 100644
> > > > --- a/virt/kvm/arm/pmu.c
> > > > +++ b/virt/kvm/arm/pmu.c
> > > > @@ -47,7 +47,10 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
> > > > counter += perf_event_read_value(pmc->perf_event, &enabled,
> > > > &running);
> > > > - return counter & pmc->bitmask;
> > > > + if (select_idx != ARMV8_PMU_CYCLE_IDX)
> > > > + counter = lower_32_bits(counter);
> > >
> > > Shouldn't this depend on PMCR.LC as well? If PMCR.LC is clear we only
> > > want the lower 32bits of the cycle counter.
> >
> > Yes that's correct. The hunk should look like this:
> >
> > - return counter & pmc->bitmask;
> > + if (!(select_idx == ARMV8_PMU_CYCLE_IDX &&
> > + __vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_LC))
> > + counter = lower_32_bits(counter);
> > +
> > + return counter;
>
> May be you could add a macro :
>
> #define vcpu_pmu_counter_is_64bit(vcpu, idx) ?
Yes I think a helper would be useful - though I'd prefer the name
'kvm_pmu_idx_is_long_cycle_counter'. This seems a little clearer as
you could otherwise argue that a chained counter is also 64 bits.
Thanks,
Andrew Murray
>
> Cheers
> Suzuki
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