[PATCH] lib: pmu: allow to use the highest available counter

[Anup Patel]

On Fri, Jun 24, 2022 at 12:33 PM Sergey Matyukevich <geomatsi at gmail.com> wrote:
>
> Hi,
>
> > Both OpenSBI and OS explicitly assume that there is no hardware counter
> > with index 1: hardware uses that bit for TM control. So OpenSBI filters
> > out that index in sanity checks.
> > However, OpenSBI doesn't consider TM bit while returning the number of
> > counters. As a result, the supervisor software is aware of less number
> > of firmware counter.
> >
> > The simple test is to make sure that there is no counter multiplexing
> > in the following command:
> >
> > $ perf stat -e \
> >         r8000000000000000,r8000000000000001,r8000000000000002,r8000000000000003, \
> >         r8000000000000004,r8000000000000005,r8000000000000006,r8000000000000007, \
> >         r8000000000000008,r8000000000000009,r800000000000000a,r800000000000000b, \
> >         r800000000000000c,r800000000000000d,r800000000000000e,r800000000000000f  \
> >         ls
> > (16 firmware events with 16 counters won't require multiplexing)
> >
> > Return accurate number of counters and update the firmware counter
>
> This is not correct.
>
> > starting index.
> >
> > Signed-off-by: Sergey Matyukevich <geomatsi at gmail.com>
> > Signed-off-by: Atish Patra <atishp at rivosinc.com>
>
> snip
>
> > -             num_hw_ctrs = sbi_hart_mhpm_count(scratch) + 2;
> > +             num_hw_ctrs = sbi_hart_mhpm_count(scratch) + 3;
> >               total_ctrs = num_hw_ctrs + SBI_PMU_FW_CTR_MAX;
> >       }
>
> I would suggest _not_ to merge this change in its current form. Current
> approach reports incorrect number of hardware counters just to make
> kernel driver provide accurate counter mask in all the subsequent
> SBI requests. That is going to impact all the other SBI implementations
> as well: all of them will have to pass incorrect hw counter number in
> order to get correct counters mask from the kernel.

Please my comments on the previous patch. I fail to see how this
patch impacts other SBI implementations. Can you elaborate more ?

Regards,
Anup

>
> Regards,
> Sergey
>
> --
> opensbi mailing list
> opensbi at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/opensbi