linux-kernel - Re: [PATCH v4 09/10] tools: lib: perf: Implement riscv mmap support

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Message-ID: <CAP-5=fU5XYXrVnRUidpwjV2LiTsdebfidL43_Qo4Z7TBxMsVGA@mail.gmail.com>
Date:   Fri, 28 Jul 2023 10:52:59 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Will Deacon <will@...nel.org>, Rob Herring <robh@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Rémi Denis-Courmont <remi@...lab.net>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Atish Patra <atishp@...osinc.com>
Subject: Re: [PATCH v4 09/10] tools: lib: perf: Implement riscv mmap support

On Thu, Jul 27, 2023 at 7:28 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>
> riscv now supports mmaping hardware counters so add what's needed to
> take advantage of that in libperf.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> Reviewed-by: Atish Patra <atishp@...osinc.com>
> ---
>  tools/lib/perf/mmap.c | 65 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>
> diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> index 0d1634cedf44..378a163f0554 100644
> --- a/tools/lib/perf/mmap.c
> +++ b/tools/lib/perf/mmap.c
> @@ -392,6 +392,71 @@ static u64 read_perf_counter(unsigned int counter)
>
>  static u64 read_timestamp(void) { return read_sysreg(cntvct_el0); }
>
> +#elif __riscv_xlen == 64

This is something of an odd guard, perhaps:
#elif defined(__riscv) && __riscv_xlen == 64

That way it is more intention revealing that this is riscv code. Could
you add a comment relating to the __riscv_xlen ?

> +
> +/* TODO: implement rv32 support */
> +
> +#define CSR_CYCLE      0xc00
> +#define CSR_TIME       0xc01
> +
> +#define csr_read(csr)                                          \
> +({                                                             \
> +       register unsigned long __v;                             \
> +               __asm__ __volatile__ ("csrr %0, " #csr          \
> +                : "=r" (__v) :                                 \
> +                : "memory");                                   \

To avoid the macro pasting that could potentially go weird, could this be:

__asm__ __volatile__ ("csrr %0, %1",
  : "=r"(__v) /* outputs */
  : "i"(csr) /* inputs */
  : "memory" /* clobbers */)

Also, why is this clobbering memory? Worth adding a comment.

Thanks,
Ian

> +                __v;                                           \
> +})
> +
> +static unsigned long csr_read_num(int csr_num)
> +{
> +#define switchcase_csr_read(__csr_num, __val)           {\
> +       case __csr_num:                                 \
> +               __val = csr_read(__csr_num);            \
> +               break; }
> +#define switchcase_csr_read_2(__csr_num, __val)         {\
> +       switchcase_csr_read(__csr_num + 0, __val)        \
> +       switchcase_csr_read(__csr_num + 1, __val)}
> +#define switchcase_csr_read_4(__csr_num, __val)         {\
> +       switchcase_csr_read_2(__csr_num + 0, __val)      \
> +       switchcase_csr_read_2(__csr_num + 2, __val)}
> +#define switchcase_csr_read_8(__csr_num, __val)         {\
> +       switchcase_csr_read_4(__csr_num + 0, __val)      \
> +       switchcase_csr_read_4(__csr_num + 4, __val)}
> +#define switchcase_csr_read_16(__csr_num, __val)        {\
> +       switchcase_csr_read_8(__csr_num + 0, __val)      \
> +       switchcase_csr_read_8(__csr_num + 8, __val)}
> +#define switchcase_csr_read_32(__csr_num, __val)        {\
> +       switchcase_csr_read_16(__csr_num + 0, __val)     \
> +       switchcase_csr_read_16(__csr_num + 16, __val)}
> +
> +       unsigned long ret = 0;
> +
> +       switch (csr_num) {
> +       switchcase_csr_read_32(CSR_CYCLE, ret)
> +       default:
> +               break;
> +       }
> +
> +       return ret;
> +#undef switchcase_csr_read_32
> +#undef switchcase_csr_read_16
> +#undef switchcase_csr_read_8
> +#undef switchcase_csr_read_4
> +#undef switchcase_csr_read_2
> +#undef switchcase_csr_read
> +}
> +
> +static u64 read_perf_counter(unsigned int counter)
> +{
> +       return csr_read_num(CSR_CYCLE + counter);
> +}
> +
> +static u64 read_timestamp(void)
> +{
> +       return csr_read_num(CSR_TIME);
> +}
> +
>  #else
>  static u64 read_perf_counter(unsigned int counter __maybe_unused) { return 0; }
>  static u64 read_timestamp(void) { return 0; }
> --
> 2.39.2
>