Re: [PATCH 0/2] perf: riscv: Preliminary Perf Event Support on RISC-V

[Alan Kao]

On Tue, Apr 03, 2018 at 03:45:17PM -0700, Palmer Dabbelt wrote:
> On Tue, 03 Apr 2018 07:29:02 PDT (-0700), alankao@xxxxxxxxxxxxx wrote:
> >On Mon, Apr 02, 2018 at 08:15:44PM -0700, Palmer Dabbelt wrote:
> >>On Mon, 02 Apr 2018 05:31:22 PDT (-0700), alankao@xxxxxxxxxxxxx wrote:
> >>>This implements the baseline PMU for RISC-V platforms.
> >>>
> >>>To ease future PMU portings, a guide is also written, containing
> >>>perf concepts, arch porting practices and some hints.
> >>>
> >>>Changes in v2:
> >>> - Fix the bug reported by Alex, which was caused by not sufficient
> >>>   initialization.  Check https://lkml.org/lkml/2018/3/31/251 for the
> >>>   discussion.
> >>>
> >>>Alan Kao (2):
> >>>  perf: riscv: preliminary RISC-V support
> >>>  perf: riscv: Add Document for Future Porting Guide
> >>>
> >>> Documentation/riscv/pmu.txt         | 249 +++++++++++++++++++
> >>> arch/riscv/Kconfig                  |  12 +
> >>> arch/riscv/include/asm/perf_event.h |  76 +++++-
> >>> arch/riscv/kernel/Makefile          |   1 +
> >>> arch/riscv/kernel/perf_event.c      | 468 ++++++++++++++++++++++++++++++++++++
> >>> 5 files changed, 802 insertions(+), 4 deletions(-)
> >>> create mode 100644 Documentation/riscv/pmu.txt
> >>> create mode 100644 arch/riscv/kernel/perf_event.c
> >>
> >>I'm having some trouble pulling this into my tree.  I think you might have
> >>another patch floating around somewhere, as I don't have any
> >>arch/riscv/include/asm/perf_event.h right now.
> >>
> >>Do you mind rebasing this on top of linux-4.16 so I can look properly?
> >>
> >>Thanks!
> >
> >Sorry for the inconvenience, but this patch was based on Alex's patch at
> >https://github.com/riscv/riscv-linux/pull/124/files.  I thought that one
> >had already been picked into your tree.
> >
> >Any ideas?
> 
> Thanks, it applies on top of that.  I'm going to play around with this a
> bit, but it looks generally good.

Note that to make it work better when wraparound occurs, you should change the
value of *.counter_width* into the width of real hardware counters.  This is
because this patch does not handle wraparound checking, so using a wider
bit mask may sometimes report a extremely large number.

Ideally this should be done by adding a Kconfig option called 
"Hifive Unleashed PMU" which automatically sets the width an reuses most of the
baseline codes.  What do you think about this?

Thanks.