Re: [PATCH V4 01/23] perf/x86: Support outputting XMM registers

[Stephane Eranian]

On Tue, Mar 26, 2019 at 9:11 AM <kan.liang@xxxxxxxxxxxxxxx> wrote:
>
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> Starting from Icelake, XMM registers can be collected in PEBS record.
> But current code only output the pt_regs.
>
> Add a new struct x86_perf_regs for both pt_regs and xmm_regs.
> XMM registers are 128 bit. To simplify the code, they are handled like
> two different registers, which means setting two bits in the register
> bitmap. This also allows only sampling the lower 64bit bits in XMM.
>
You are adding this new x86_perf_regs struct but the patch does not
include how it is allocated.
I don't see from this patch where x86_perf_regs->xmm_regs is actually allocated.

> The index of XMM registers starts from 32. There are 16 XMM registers.
> So all reserved space for regs are used. Remove REG_RESERVED.
>
> Add PERF_REG_X86_XMM_MAX, which stands for the max number of all x86
> regs including both GPRs and XMM.
>
> XMM is not supported on all platforms. Adding has_xmm_regs to indicate
> the specific platform. Also add checks in x86_pmu_hw_config() to reject
> invalid config of regs_user and regs_intr.
>
> Add REG_NOSUPPORT for 32bit to exclude unsupported registers.
>
> Originally-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
>
> Changes since V3:
> - Keep the old names for GPRs. Rename PERF_REG_X86_MAX to
>   PERF_REG_X86_XMM_MAX
> - Remove unnecessary REG_RESERVED
> - Add REG_NOSUPPORT for 32bit
>
>  arch/x86/events/core.c                | 10 ++++++++++
>  arch/x86/events/perf_event.h          |  2 ++
>  arch/x86/include/asm/perf_event.h     |  5 +++++
>  arch/x86/include/uapi/asm/perf_regs.h | 23 ++++++++++++++++++++++-
>  arch/x86/kernel/perf_regs.c           | 27 ++++++++++++++++++++-------
>  5 files changed, 59 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index e2b1447192a8..9378c6b2128f 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -560,6 +560,16 @@ int x86_pmu_hw_config(struct perf_event *event)
>                         return -EINVAL;
>         }
>
> +       if (event->attr.sample_regs_user & ~PEBS_REGS)
> +               return -EINVAL;
> +       /*
> +        * Besides the general purpose registers, XMM registers may
> +        * be collected in PEBS on some platforms, e.g. Icelake
> +        */
> +       if ((event->attr.sample_regs_intr & ~PEBS_REGS) &&
> +           (!x86_pmu.has_xmm_regs || !event->attr.precise_ip))
> +               return -EINVAL;
> +
Shouldn't you be testing on PEBS_REGS only if the user is asking for
PEBS sampling?
That is not because PEBS may not capture a register that the kernel
could not do it
without PEBS.

>         return x86_setup_perfctr(event);
>  }
>
> diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
> index a75955741c50..6428941a5073 100644
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -657,6 +657,8 @@ struct x86_pmu {
>          * Check period value for PERF_EVENT_IOC_PERIOD ioctl.
>          */
>         int (*check_period) (struct perf_event *event, u64 period);
> +
> +       unsigned int    has_xmm_regs : 1; /* support XMM regs */
>  };
Is this an Intel specific field? If so, then say intel_has_xmm_regs,
just like amd_nb_constraints above.
If not, then define what is is supposed to mean? Because I am sure
there is another way to detect if
the CPU support XMM regs, like cpufeatures?

>
>  struct x86_perf_task_context {
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 8bdf74902293..d9f5bbe44b3c 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -248,6 +248,11 @@ extern void perf_events_lapic_init(void);
>  #define PERF_EFLAGS_VM         (1UL << 5)
>
>  struct pt_regs;
> +struct x86_perf_regs {
> +       struct pt_regs  regs;
> +       u64             *xmm_regs;
> +};
> +
>  extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
>  extern unsigned long perf_misc_flags(struct pt_regs *regs);
>  #define perf_misc_flags(regs)  perf_misc_flags(regs)
> diff --git a/arch/x86/include/uapi/asm/perf_regs.h b/arch/x86/include/uapi/asm/perf_regs.h
> index f3329cabce5c..ac67bbea10ca 100644
> --- a/arch/x86/include/uapi/asm/perf_regs.h
> +++ b/arch/x86/include/uapi/asm/perf_regs.h
> @@ -27,8 +27,29 @@ enum perf_event_x86_regs {
>         PERF_REG_X86_R13,
>         PERF_REG_X86_R14,
>         PERF_REG_X86_R15,
> -
> +       /* These are the limits for the GPRs. */
>         PERF_REG_X86_32_MAX = PERF_REG_X86_GS + 1,
>         PERF_REG_X86_64_MAX = PERF_REG_X86_R15 + 1,
> +
> +       /* These all need two bits set because they are 128bit */
> +       PERF_REG_X86_XMM0  = 32,
> +       PERF_REG_X86_XMM1  = 34,
> +       PERF_REG_X86_XMM2  = 36,
> +       PERF_REG_X86_XMM3  = 38,
> +       PERF_REG_X86_XMM4  = 40,
> +       PERF_REG_X86_XMM5  = 42,
> +       PERF_REG_X86_XMM6  = 44,
> +       PERF_REG_X86_XMM7  = 46,
> +       PERF_REG_X86_XMM8  = 48,
> +       PERF_REG_X86_XMM9  = 50,
> +       PERF_REG_X86_XMM10 = 52,
> +       PERF_REG_X86_XMM11 = 54,
> +       PERF_REG_X86_XMM12 = 56,
> +       PERF_REG_X86_XMM13 = 58,
> +       PERF_REG_X86_XMM14 = 60,
> +       PERF_REG_X86_XMM15 = 62,
> +
> +       /* These include both GPRs and XMMX registers */
> +       PERF_REG_X86_XMM_MAX = PERF_REG_X86_XMM15 + 2,
>  };
>  #endif /* _ASM_X86_PERF_REGS_H */
> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
> index c06c4c16c6b6..07c30ee17425 100644
> --- a/arch/x86/kernel/perf_regs.c
> +++ b/arch/x86/kernel/perf_regs.c
> @@ -59,18 +59,34 @@ static unsigned int pt_regs_offset[PERF_REG_X86_MAX] = {
>
>  u64 perf_reg_value(struct pt_regs *regs, int idx)
>  {
> +       struct x86_perf_regs *perf_regs;
> +
> +       if (idx >= PERF_REG_X86_XMM0 && idx < PERF_REG_X86_XMM_MAX) {
> +               perf_regs = container_of(regs, struct x86_perf_regs, regs);
> +               if (!perf_regs->xmm_regs)
> +                       return 0;
> +               return perf_regs->xmm_regs[idx - PERF_REG_X86_XMM0];
> +       }
> +
>         if (WARN_ON_ONCE(idx >= ARRAY_SIZE(pt_regs_offset)))
>                 return 0;
>
>         return regs_get_register(regs, pt_regs_offset[idx]);
>  }
>
> -#define REG_RESERVED (~((1ULL << PERF_REG_X86_MAX) - 1ULL))
> -
>  #ifdef CONFIG_X86_32
> +#define REG_NOSUPPORT ((1ULL << PERF_REG_X86_R8) | \
> +                      (1ULL << PERF_REG_X86_R9) | \
> +                      (1ULL << PERF_REG_X86_R10) | \
> +                      (1ULL << PERF_REG_X86_R11) | \
> +                      (1ULL << PERF_REG_X86_R12) | \
> +                      (1ULL << PERF_REG_X86_R13) | \
> +                      (1ULL << PERF_REG_X86_R14) | \
> +                      (1ULL << PERF_REG_X86_R15))
> +
>  int perf_reg_validate(u64 mask)
>  {
> -       if (!mask || mask & REG_RESERVED)
> +       if (!mask || (mask & REG_NOSUPPORT))
>                 return -EINVAL;
>
>         return 0;
> @@ -96,10 +112,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
>
>  int perf_reg_validate(u64 mask)
>  {
> -       if (!mask || mask & REG_RESERVED)
> -               return -EINVAL;
> -
> -       if (mask & REG_NOSUPPORT)
> +       if (!mask || (mask & REG_NOSUPPORT))
>                 return -EINVAL;
>
>         return 0;
> --
> 2.17.1
>