[PATCH] lib: sbi: Bypass CY and IR bit setting in mcountinhibit

[Atish Patra]

On Wed, Nov 16, 2022 at 6:57 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 16 Nov 2022, at 10:18, Eric Lin <eric.lin at sifive.com> wrote:
> >
> > CYCLE and INSTRET counters are part of uABI and they were
> > re-enable for userspace in Linux riscv pmu driver.
> >
> > To make these counters increase normally in userspace, we bypass
> > CY and IR bit checking when setting mcountinhibit register.
> >
> > LINK:https://lore.kernel.org/all/20220928131807.30386-1-palmer@rivosinc.com/
> > Signed-off-by: Eric Lin <eric.lin at sifive.com>
>
> If Linux is making SBI calls it doesn’t want then it should stop making
> those calls. S-mode requesting CY and IR inhibit bits be set is totally
> legitimate in some circumstances, it’s not up to firmware to enforce a
> specific S-mode OS policy.
>

Yes. Start/sop is required when the user is doing perf stat or record
for these counters.

To increase the CYCLE and INSTRET,
pmu_sbi_starting_cpu( in drivers/perf/riscv_pmu_sbi.c)
should be modified to stop only the programmable counters. Not all.

> Jess
>
> > ---
> > lib/sbi/sbi_pmu.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/sbi/sbi_pmu.c b/lib/sbi/sbi_pmu.c
> > index 91d9ccc..28107e5 100644
> > --- a/lib/sbi/sbi_pmu.c
> > +++ b/lib/sbi/sbi_pmu.c
> > @@ -318,7 +318,7 @@ static int pmu_ctr_start_hw(uint32_t cidx, uint64_t ival, bool ival_update)
> >       if (cidx >= num_hw_ctrs || cidx == 1)
> >               return SBI_EINVAL;
> >
> > -     if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11)
> > +     if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11 || cidx == 0 || cidx == 2)
> >               goto skip_inhibit_update;
> >
> >       /*
> > @@ -413,7 +413,7 @@ static int pmu_ctr_stop_hw(uint32_t cidx)
> >       struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
> >       unsigned long mctr_inhbt;
> >
> > -     if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11)
> > +     if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11 || cidx == 0 || cidx == 2)
> >               return 0;
> >
> >       mctr_inhbt = csr_read(CSR_MCOUNTINHIBIT);
> > --
> > 2.36.1
> >
> >
> > --
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> > opensbi at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/opensbi
>
>
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-- 
Regards,
Atish