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

Alexandre Ghiti
2023-07-31T10:15:29Z

Hi Ian,

On Fri, Jul 28, 2023 at 7:53 PM Ian Rogers <irogers@google.com> wrote:
>
> On Thu, Jul 27, 2023 at 7:28 AM Alexandre Ghiti <alexghiti@rivosinc.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@rivosinc.com>
> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> > Reviewed-by: Atish Patra <atishp@rivosinc.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 ?

I guess Andrew answered that already.

>
> > +
> > +/* 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.

No idea, I see that it is also done this way in
arch/riscv/include/asm/csr.h. @Atish Kumar Patra , @Palmer Dabbelt ?

Thanks for your comments!

Alex

>
> 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
> >