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

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Message-ID: <mhng-5b2192d4-d400-439a-839e-882f708b15b9@palmer-si-x1c4>
Date:   Thu, 05 Apr 2018 09:29:08 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     alankao@...estech.com
CC:     albert@...ive.com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, sols@...ive.com,
        corbet@....net, linux-riscv@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH 0/2] perf: riscv: Preliminary Perf Event Support on RISC-V

On Wed, 04 Apr 2018 22:02:29 PDT (-0700), alankao@...estech.com wrote:
> On Tue, Apr 03, 2018 at 03:45:17PM -0700, Palmer Dabbelt wrote:
>> On Tue, 03 Apr 2018 07:29:02 PDT (-0700), alankao@...estech.com 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@...estech.com 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?

We're working through this now :)