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Date: Mon, 2 Oct 2023 09:49:55 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
linux-kernel@...r.kernel.org
Cc: mark.rutland@....com, alexander.shishkin@...ux.intel.com,
jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
adrian.hunter@...el.com, ak@...ux.intel.com, eranian@...gle.com,
alexey.v.bayduraev@...ux.intel.com, tinghao.zhang@...el.com,
Sandipan Das <sandipan.das@....com>,
Ravi Bangoria <ravi.bangoria@....com>,
Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
Subject: Re: [RESEND PATCH V3 1/6] perf: Add branch stack extra
Hi Peter,
Could you please share your comments for this series?
Thanks,
Kan
On 2023-09-11 11:48 a.m., kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> Currently, the additional information of a branch entry is stored in a
> u64 space. With more and more information added, the space is running
> out. For example, the information of occurrences of events will be added
> for each branch.
>
> Add a new branch sample type, PERF_SAMPLE_BRANCH_EXTRA, to indicate
> whether to support an extra space.
>
> Two places were suggested to append the extra space.
> https://lore.kernel.org/lkml/20230802215814.GH231007@hirez.programming.kicks-ass.net/
> One place is right after the flags of each branch entry. It changes the
> existing struct perf_branch_entry. In the later Intel-specific
> implementation, two separate spaces have to be created in the
> struct cpu_hw_events to store different branch entry structures. That
> duplicates space.
> The other place is right after the entire struct perf_branch_stack.
> Only adding the new extra space in the struct cpu_hw_event is necessary.
> The disadvantage is that the pointer of the extra space has to be
> recorded. The common interface perf_sample_save_brstack() has to be
> updated as well.
>
> The latter requires less space and is much straight forward. It is
> implemented in the patch.
>
> Also, add a new branch sample type, PERF_SAMPLE_BRANCH_EVT_CNTRS, to
> indicate whether include occurrences of events in branch info. The
> information will be stored in the extra space.
>
> Add two helper functions for the new branch sample types.
>
> Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Sandipan Das <sandipan.das@....com>
> Cc: Ravi Bangoria <ravi.bangoria@....com>
> Cc: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
> ---
>
> Changes since V2:
> - Drop the new bit in struct perf_branch_entry
> - Introduce a new sample type PERF_SAMPLE_BRANCH_EXTRA
>
> arch/powerpc/perf/core-book3s.c | 2 +-
> arch/x86/events/amd/core.c | 2 +-
> arch/x86/events/core.c | 2 +-
> arch/x86/events/intel/core.c | 2 +-
> arch/x86/events/intel/ds.c | 4 ++--
> include/linux/perf_event.h | 22 +++++++++++++++++++++-
> include/uapi/linux/perf_event.h | 9 +++++++++
> kernel/events/core.c | 8 ++++++++
> 8 files changed, 44 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 8c1f7def596e..3c14596bbfaf 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2313,7 +2313,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
> struct cpu_hw_events *cpuhw;
> cpuhw = this_cpu_ptr(&cpu_hw_events);
> power_pmu_bhrb_read(event, cpuhw);
> - perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack);
> + perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack, NULL);
> }
>
> if (event->attr.sample_type & PERF_SAMPLE_DATA_SRC &&
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index abadd5f23425..01c0619d12d5 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -930,7 +930,7 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs)
> continue;
>
> if (has_branch_stack(event))
> - perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> + perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>
> if (perf_event_overflow(event, &data, regs))
> x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 185f902e5f28..2919bb5a53a0 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1702,7 +1702,7 @@ int x86_pmu_handle_irq(struct pt_regs *regs)
> perf_sample_data_init(&data, 0, event->hw.last_period);
>
> if (has_branch_stack(event))
> - perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> + perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>
> if (perf_event_overflow(event, &data, regs))
> x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 64a3533997e1..0f4ce79de4f8 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3058,7 +3058,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
> perf_sample_data_init(&data, 0, event->hw.last_period);
>
> if (has_branch_stack(event))
> - perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> + perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>
> if (perf_event_overflow(event, &data, regs))
> x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index eb8dd8b8a1e8..7566190389f0 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1755,7 +1755,7 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event,
> setup_pebs_time(event, data, pebs->tsc);
>
> if (has_branch_stack(event))
> - perf_sample_save_brstack(data, event, &cpuc->lbr_stack);
> + perf_sample_save_brstack(data, event, &cpuc->lbr_stack, NULL);
> }
>
> static void adaptive_pebs_save_regs(struct pt_regs *regs,
> @@ -1912,7 +1912,7 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
>
> if (has_branch_stack(event)) {
> intel_pmu_store_pebs_lbrs(lbr);
> - perf_sample_save_brstack(data, event, &cpuc->lbr_stack);
> + perf_sample_save_brstack(data, event, &cpuc->lbr_stack, NULL);
> }
> }
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index e83f13ce4a9f..c4877924d43c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1137,6 +1137,15 @@ static inline bool branch_sample_priv(const struct perf_event *event)
> return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_PRIV_SAVE;
> }
>
> +static inline bool branch_sample_extra(const struct perf_event *event)
> +{
> + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_EXTRA;
> +}
> +
> +static inline bool branch_sample_evt_cntrs(const struct perf_event *event)
> +{
> + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_EVT_CNTRS;
> +}
>
> struct perf_sample_data {
> /*
> @@ -1171,6 +1180,7 @@ struct perf_sample_data {
> struct perf_callchain_entry *callchain;
> struct perf_raw_record *raw;
> struct perf_branch_stack *br_stack;
> + u64 *br_stack_ext;
> union perf_sample_weight weight;
> union perf_mem_data_src data_src;
> u64 txn;
> @@ -1248,7 +1258,8 @@ static inline void perf_sample_save_raw_data(struct perf_sample_data *data,
>
> static inline void perf_sample_save_brstack(struct perf_sample_data *data,
> struct perf_event *event,
> - struct perf_branch_stack *brs)
> + struct perf_branch_stack *brs,
> + u64 *brs_ext)
> {
> int size = sizeof(u64); /* nr */
>
> @@ -1256,7 +1267,16 @@ static inline void perf_sample_save_brstack(struct perf_sample_data *data,
> size += sizeof(u64);
> size += brs->nr * sizeof(struct perf_branch_entry);
>
> + /*
> + * The extension space is appended after the struct perf_branch_stack.
> + * It is used to store the extra data of each branch, e.g.,
> + * the occurrences of events since the last branch entry for Intel LBR.
> + */
> + if (branch_sample_extra(event))
> + size += brs->nr * sizeof(u64);
> +
> data->br_stack = brs;
> + data->br_stack_ext = brs_ext;
> data->dyn_size += size;
> data->sample_flags |= PERF_SAMPLE_BRANCH_STACK;
> }
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 39c6a250dd1b..252066579dae 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -204,6 +204,10 @@ enum perf_branch_sample_type_shift {
>
> PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT = 18, /* save privilege mode */
>
> + PERF_SAMPLE_BRANCH_EXTRA_SHIFT = 19, /* support extra space */
> +
> + PERF_SAMPLE_BRANCH_EVT_CNTRS_SHIFT = 20, /* save occurrences of events on a branch */
> +
> PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */
> };
>
> @@ -235,6 +239,10 @@ enum perf_branch_sample_type {
>
> PERF_SAMPLE_BRANCH_PRIV_SAVE = 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT,
>
> + PERF_SAMPLE_BRANCH_EXTRA = 1U << PERF_SAMPLE_BRANCH_EXTRA_SHIFT,
> +
> + PERF_SAMPLE_BRANCH_EVT_CNTRS = 1U << PERF_SAMPLE_BRANCH_EVT_CNTRS_SHIFT,
> +
> PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> };
>
> @@ -982,6 +990,7 @@ enum perf_event_type {
> * { u64 nr;
> * { u64 hw_idx; } && PERF_SAMPLE_BRANCH_HW_INDEX
> * { u64 from, to, flags } lbr[nr];
> + * { u64 extra; } ext[nr] && PERF_SAMPLE_BRANCH_EXTRA
> * } && PERF_SAMPLE_BRANCH_STACK
> *
> * { u64 abi; # enum perf_sample_regs_abi
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f84e2640ea2f..482e7efe365c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7324,6 +7324,14 @@ void perf_output_sample(struct perf_output_handle *handle,
> if (branch_sample_hw_index(event))
> perf_output_put(handle, data->br_stack->hw_idx);
> perf_output_copy(handle, data->br_stack->entries, size);
> + /*
> + * Add the extension space which is appended
> + * right after the struct perf_branch_stack.
> + */
> + if (branch_sample_extra(event) && data->br_stack_ext) {
> + size = data->br_stack->nr * sizeof(u64);
> + perf_output_copy(handle, data->br_stack_ext, size);
> + }
> } else {
> /*
> * we always store at least the value of nr
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