linux-kernel - Re: [PATCH v8 08/24] drivers/perf: riscv: Fix counter mask iteration for RV32

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Message-ID: <CAHBxVyHZ81G7yaMkV25RBwS=ric=MA92MePaPtQaOXuR+C70YA@mail.gmail.com>
Date: Fri, 19 Apr 2024 18:08:12 -0700
From: Atish Kumar Patra <atishp@...osinc.com>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: linux-kernel@...r.kernel.org, Andrew Jones <ajones@...tanamicro.com>, 
	Ajay Kaher <ajay.kaher@...adcom.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, Anup Patel <anup@...infault.org>, 
	Conor Dooley <conor.dooley@...rochip.com>, Juergen Gross <jgross@...e.com>, 
	kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Shuah Khan <shuah@...nel.org>, virtualization@...ts.linux.dev, 
	Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v8 08/24] drivers/perf: riscv: Fix counter mask iteration
 for RV32

On Fri, Apr 19, 2024 at 5:37 PM Samuel Holland
<samuel.holland@...ive.com> wrote:
>
> Hi Atish,
>
> On 2024-04-20 10:17 AM, Atish Patra wrote:
> > For RV32, used_hw_ctrs can have more than 1 word if the firmware chooses
> > to interleave firmware/hardware counters indicies. Even though it's a
> > unlikely scenario, handle that case by iterating over all the words
> > instead of just using the first word.
> >
> > Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> > Signed-off-by: Atish Patra <atishp@...osinc.com>
> > ---
> >  drivers/perf/riscv_pmu_sbi.c | 21 ++++++++++++---------
> >  1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> > index f23501898657..4eacd89141a9 100644
> > --- a/drivers/perf/riscv_pmu_sbi.c
> > +++ b/drivers/perf/riscv_pmu_sbi.c
> > @@ -652,10 +652,12 @@ static inline void pmu_sbi_stop_all(struct riscv_pmu *pmu)
> >  static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
> >  {
> >       struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
> > +     int i;
> >
> > -     /* No need to check the error here as we can't do anything about the error */
> > -     sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, 0,
> > -               cpu_hw_evt->used_hw_ctrs[0], 0, 0, 0, 0);
> > +     for (i = 0; i < BITS_TO_LONGS(RISCV_MAX_COUNTERS); i++)
> > +             /* No need to check the error here as we can't do anything about the error */
> > +             sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, i * BITS_PER_LONG,
> > +                       cpu_hw_evt->used_hw_ctrs[i], 0, 0, 0, 0);
> >  }
> >
> >  /*
> > @@ -667,7 +669,7 @@ static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
> >  static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
> >                                              unsigned long ctr_ovf_mask)
> >  {
> > -     int idx = 0;
> > +     int idx = 0, i;
> >       struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
> >       struct perf_event *event;
> >       unsigned long flag = SBI_PMU_START_FLAG_SET_INIT_VALUE;
> > @@ -676,11 +678,12 @@ static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
> >       struct hw_perf_event *hwc;
> >       u64 init_val = 0;
> >
> > -     ctr_start_mask = cpu_hw_evt->used_hw_ctrs[0] & ~ctr_ovf_mask;
> > -
> > -     /* Start all the counters that did not overflow in a single shot */
> > -     sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, 0, ctr_start_mask,
> > -               0, 0, 0, 0);
> > +     for (i = 0; i < BITS_TO_LONGS(RISCV_MAX_COUNTERS); i++) {
> > +             ctr_start_mask = cpu_hw_evt->used_hw_ctrs[i] & ~ctr_ovf_mask;
>
> This is applying the mask for the first 32 logical counters to the both sets of
> 32 logical counters. ctr_ovf_mask needs to be 64 bits wide here, so each loop
> iteration can apply the correct half of the mask.
>

The 64bit wide support for ctr_ovf_mask is added in the next patch.

> Regards,
> Samuel
>
> > +             /* Start all the counters that did not overflow in a single shot */
> > +             sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, i * BITS_PER_LONG, ctr_start_mask,
> > +                     0, 0, 0, 0);
> > +     }
> >
> >       /* Reinitialize and start all the counter that overflowed */
> >       while (ctr_ovf_mask) {
>