linux-kernel - Re: [PATCH V2 2/6] perf: Add branch stack extension

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Date:   Tue, 23 May 2023 11:33:54 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     kan.liang@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, 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,
        Ravi Bangoria <ravi.bangoria@....com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
Subject: Re: [PATCH V2 2/6] perf: Add branch stack extension

Hi Kan,

On 5/22/2023 5:00 PM, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Currently, the extra 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 an extension space to record the new information for each branch
> entry. The space is appended after the struct perf_branch_stack.
> 
> Add a bit in struct perf_branch_entry to indicate whether the extra
> information is included.
> 
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> 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>
> ---
> 
> New patch
> - Introduce a generic extension space which can be used to
>   store the LBR event information for Intel. It can also be used by
>   other ARCHs for the other purpose.
> - Add a new bit in struct perf_branch_entry to indicate whether the
>   extra information is included.
> 
>  arch/powerpc/perf/core-book3s.c |  2 +-
>  arch/x86/events/amd/core.c      |  2 +-
>  arch/x86/events/intel/core.c    |  2 +-
>  arch/x86/events/intel/ds.c      |  4 ++--
>  include/linux/perf_event.h      | 18 +++++++++++++++++-
>  include/uapi/linux/perf_event.h |  4 +++-
>  kernel/events/core.c            |  5 +++++
>  7 files changed, 30 insertions(+), 7 deletions(-)
> 

This seems to be missing the following:

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 6310fc5c9f52..b6739f63dc34 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1704,7 +1704,7 @@ 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);


Otherwise, the changes look good to me.

Reviewed-by: Sandipan Das <sandipan.das@....com>