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Date: Tue, 19 Nov 2019 11:02:10 -0800
From: Stephane Eranian <eranian@...gle.com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
vitaly.slobodskoy@...el.com, pavel.gerasimov@...el.com,
Andi Kleen <ak@...ux.intel.com>,
Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH V4 01/13] perf/core: Add new branch sample type for LBR TOS
On Tue, Nov 19, 2019 at 6:35 AM <kan.liang@...ux.intel.com> wrote:
>
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> 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@...ux.intel.com>
> ---
> 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
>
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