linux-kernel - Re: [RFC PATCH 0/6] Support raw event and DT for perf on RISC-V

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Message-ID: <CANXhq0p_HoD6npHmoxxYHohBsgihfe5S-0DG04xLpQ3VO1w7oQ@mail.gmail.com>
Date:   Mon, 29 Jun 2020 13:52:15 +0800
From:   Zong Li <zong.li@...ive.com>
To:     Anup Patel <anup@...infault.org>, alankao@...estech.com
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/6] Support raw event and DT for perf on RISC-V

On Mon, Jun 29, 2020 at 12:53 PM Anup Patel <anup@...infault.org> wrote:
>
> On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li@...ive.com> wrote:
> >
> > This patch set adds raw event support on RISC-V. In addition, we
> > introduce the DT mechanism to make our perf more generic and common.
> >
> > Currently, we set the hardware events by writing the mhpmeventN CSRs, it
> > would raise an illegal instruction exception and trap into m-mode to
> > emulate event selector CSRs access. It doesn't make sense because we
> > shouldn't write the m-mode CSRs in s-mode. Ideally, we should set event
> > selector through standard SBI call or the shadow CSRs of s-mode. We have
> > prepared a proposal of a new SBI extension, called "PMU SBI extension",
> > but we also discussing the feasibility of accessing these PMU CSRs on
> > s-mode at the same time, such as delegation mechanism, so I was
> > wondering if we could use SBI calls first and make the PMU SBI extension
> > as legacy when s-mode access mechanism is accepted by Foundation? or
> > keep the current situation to see what would happen in the future.
> >
> > This patch set also introduces the DT mechanism, we don't want to add too
> > much platform-dependency code in perf like other architectures, so we
> > put the mapping of generic hardware events to DT, then we can easy to
> > transfer generic hardware events to vendor's own hardware events without
> > any platfrom-dependency stuff in our perf.
>
> Please re-write this series to have RISC-V PMU driver as a regular
> platform driver as drivers/perf/riscv_pmu.c.
>
> The PMU related sources will have to be removed from arch/riscv.
>
> Based on implementation of final drivers/perf/riscv_pmu.c we will
> come-up with drivers/perf/riscv_sbi_pmu.c driver for SBI perf counters.
>

There are some different ways to implement perf, and current
implementation seems to be consensus when perf was introduced at the
beginning [0][1]. I don't persist to which one, I could change the
implementation as you mentioned if it is a new consensus one.

[0] https://github.com/riscv/riscv-linux/pull/124#issuecomment-367563910
[1] https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/f19TmCNP6yA

> Regards,
> Anup
>
> >
> > Zong Li (6):
> >   dt-bindings: riscv: Add YAML documentation for PMU
> >   riscv: dts: sifive: Add DT support for PMU
> >   riscv: add definition of hpmcounter CSRs
> >   riscv: perf: Add raw event support
> >   riscv: perf: introduce DT mechanism
> >   riscv: remove PMU menu of Kconfig
> >
> >  .../devicetree/bindings/riscv/pmu.yaml        |  59 +++
> >  arch/riscv/Kconfig                            |  13 -
> >  arch/riscv/boot/dts/sifive/fu540-c000.dtsi    |  13 +
> >  arch/riscv/include/asm/csr.h                  |  58 +++
> >  arch/riscv/include/asm/perf_event.h           | 100 ++--
> >  arch/riscv/kernel/Makefile                    |   2 +-
> >  arch/riscv/kernel/perf_event.c                | 471 +++++++++++-------
> >  7 files changed, 471 insertions(+), 245 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/riscv/pmu.yaml
> >
> > --
> > 2.27.0
> >