Re: [PATCH V4 01/13] perf/core: Add new branch sample type for LBR TOS

[Stephane Eranian]

On Tue, Nov 19, 2019 at 6:35 AM <kan.liang@xxxxxxxxxxxxxxx> wrote:
>
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> In LBR call stack mode, the depth of reconstructed LBR call stack limits
> to the number of LBR registers. With LBR Top-of-Stack (TOS) information,
> perf tool may stitch the stacks of two samples. The reconstructed LBR
> call stack can break the HW limitation.
>
> Add a new branch sample type to retrieve LBR TOS. The new type is PMU
> specific. Add it at the end of enum perf_branch_sample_type.
> Add a macro to retrieve defined bits of branch sample type.
> Update perf_copy_attr() to handle the new bit.
>
> Only when the new branch sample type is set, the TOS information is
> dumped into the PERF_SAMPLE_BRANCH_STACK output.
> Perf tool should check the attr.branch_sample_type, and apply the
> corresponding format for PERF_SAMPLE_BRANCH_STACK samples.
> Otherwise, some user case may be broken. For example, users may parse a
> perf.data, which include the new branch sample type, with an old version
> perf tool (without the check). Users probably get incorrect information
> without any warning.
>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
>  include/linux/perf_event.h      |  2 ++
>  include/uapi/linux/perf_event.h | 16 ++++++++++++++--
>  kernel/events/core.c            | 13 ++++++++++++-
>  3 files changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 011dcbdbccc2..761021c7ee8a 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -93,6 +93,7 @@ struct perf_raw_record {
>  /*
>   * branch stack layout:
>   *  nr: number of taken branches stored in entries[]
> + *  tos: Top-of-Stack (TOS) information. PMU specific data.
>   *
>   * Note that nr can vary from sample to sample
>   * branches (to, from) are stored from most recent
> @@ -101,6 +102,7 @@ struct perf_raw_record {
>   */
>  struct perf_branch_stack {
>         __u64                           nr;
> +       __u64                           tos; /* PMU specific data */
>         struct perf_branch_entry        entries[0];
>  };
>
Same remark as with the other patch. You need to abstract this.
The TOS and PMU specific data should be limited to  x86/event/intel/*.[ch].

> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index bb7b271397a6..c2da61c9ace7 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -180,7 +180,10 @@ enum perf_branch_sample_type_shift {
>
>         PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT      = 16, /* save branch type */
>
> -       PERF_SAMPLE_BRANCH_MAX_SHIFT            /* non-ABI */
> +       PERF_SAMPLE_BRANCH_MAX_SHIFT            = 17, /* non-ABI */
> +
> +       /* PMU specific */
> +       PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT        = 63, /* save LBR TOS */
>  };
>
>  enum perf_branch_sample_type {
> @@ -208,8 +211,13 @@ enum perf_branch_sample_type {
>                 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
>
>         PERF_SAMPLE_BRANCH_MAX          = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> +
> +       PERF_SAMPLE_BRANCH_LBR_TOS      = 1ULL << PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT,
>  };
>
> +#define PERF_SAMPLE_BRANCH_MASK                ((PERF_SAMPLE_BRANCH_MAX - 1) |\
> +                                        PERF_SAMPLE_BRANCH_LBR_TOS)
> +
>  /*
>   * Common flow change classification
>   */
> @@ -849,7 +857,11 @@ enum perf_event_type {
>          *        char                  data[size];}&& PERF_SAMPLE_RAW
>          *
>          *      { u64                   nr;
> -        *        { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK
> +        *        { u64 from, to, flags } lbr[nr];
> +        *
> +        *        # only available if PERF_SAMPLE_BRANCH_LBR_TOS is set
> +        *        u64                   tos;
> +        *      } && PERF_SAMPLE_BRANCH_STACK
>          *
>          *      { u64                   abi; # enum perf_sample_regs_abi
>          *        u64                   regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index cfd89b4a02d8..8aff3aad43b5 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6391,6 +6391,11 @@ static void perf_output_read(struct perf_output_handle *handle,
>                 perf_output_read_one(handle, event, enabled, running);
>  }
>
> +static inline bool perf_sample_save_lbr_tos(struct perf_event *event)
> +{
> +       return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_LBR_TOS;
> +}
> +
>  void perf_output_sample(struct perf_output_handle *handle,
>                         struct perf_event_header *header,
>                         struct perf_sample_data *data,
> @@ -6480,6 +6485,8 @@ void perf_output_sample(struct perf_output_handle *handle,
>
>                         perf_output_put(handle, data->br_stack->nr);
>                         perf_output_copy(handle, data->br_stack->entries, size);
> +                       if (perf_sample_save_lbr_tos(event))
> +                               perf_output_put(handle, data->br_stack->tos);
>                 } else {
>                         /*
>                          * we always store at least the value of nr
> @@ -6667,7 +6674,11 @@ void perf_prepare_sample(struct perf_event_header *header,
>                 if (data->br_stack) {
>                         size += data->br_stack->nr
>                               * sizeof(struct perf_branch_entry);
> +
> +                       if (perf_sample_save_lbr_tos(event))
> +                               size += sizeof(u64);
>                 }
> +
>                 header->size += size;
>         }
>
> @@ -10731,7 +10742,7 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
>                 u64 mask = attr->branch_sample_type;
>
>                 /* only using defined bits */
> -               if (mask & ~(PERF_SAMPLE_BRANCH_MAX-1))
> +               if (mask & ~PERF_SAMPLE_BRANCH_MASK)
>                         return -EINVAL;
>
>                 /* at least one branch bit must be set */
> --
> 2.17.1
>