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Date:   Fri, 10 Nov 2023 22:09:02 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Indu Bhagat <indu.bhagat@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH RFC 01/10] perf: Remove get_perf_callchain() 'init_nr' argument

Hello,

On Wed, Nov 8, 2023 at 4:43 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> The 'init_nr' argument has double duty: it's used to initialize both the
> number of contexts and the number of stack entries.  That's confusing
> and the callers always pass zero anyway.  Hard code the zero.

IIRC it was used to skip a number of first stack entries in BPF.
I changed the code to not use init_nr but forgot to update
the perf code.

Acked-by: Namhyung Kim <Namhyung@...nel.org>

Thanks,
Namhyung

>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  include/linux/perf_event.h |  2 +-
>  kernel/bpf/stackmap.c      |  4 ++--
>  kernel/events/callchain.c  | 12 ++++++------
>  kernel/events/core.c       |  2 +-
>  4 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index afb028c54f33..f4b05954076c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1533,7 +1533,7 @@ DECLARE_PER_CPU(struct perf_callchain_entry, perf_callchain_entry);
>  extern void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs);
>  extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs);
>  extern struct perf_callchain_entry *
> -get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
> +get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
>                    u32 max_stack, bool crosstask, bool add_mark);
>  extern int get_callchain_buffers(int max_stack);
>  extern void put_callchain_buffers(void);
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index d6b277482085..b0b0fbff7c18 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -294,7 +294,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
>         if (max_depth > sysctl_perf_event_max_stack)
>                 max_depth = sysctl_perf_event_max_stack;
>
> -       trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
> +       trace = get_perf_callchain(regs, kernel, user, max_depth,
>                                    false, false);
>
>         if (unlikely(!trace))
> @@ -420,7 +420,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
>         else if (kernel && task)
>                 trace = get_callchain_entry_for_task(task, max_depth);
>         else
> -               trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
> +               trace = get_perf_callchain(regs, kernel, user, max_depth,
>                                            false, false);
>         if (unlikely(!trace))
>                 goto err_fault;
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 1273be84392c..1e135195250c 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -177,7 +177,7 @@ put_callchain_entry(int rctx)
>  }
>
>  struct perf_callchain_entry *
> -get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
> +get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
>                    u32 max_stack, bool crosstask, bool add_mark)
>  {
>         struct perf_callchain_entry *entry;
> @@ -188,11 +188,11 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
>         if (!entry)
>                 return NULL;
>
> -       ctx.entry     = entry;
> -       ctx.max_stack = max_stack;
> -       ctx.nr        = entry->nr = init_nr;
> -       ctx.contexts       = 0;
> -       ctx.contexts_maxed = false;
> +       ctx.entry               = entry;
> +       ctx.max_stack           = max_stack;
> +       ctx.nr                  = entry->nr = 0;
> +       ctx.contexts            = 0;
> +       ctx.contexts_maxed      = false;
>
>         if (kernel && !user_mode(regs)) {
>                 if (add_mark)
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 683dc086ef10..b0d62df7df4e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7600,7 +7600,7 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
>         if (!kernel && !user)
>                 return &__empty_callchain;
>
> -       callchain = get_perf_callchain(regs, 0, kernel, user,
> +       callchain = get_perf_callchain(regs, kernel, user,
>                                        max_stack, crosstask, true);
>         return callchain ?: &__empty_callchain;
>  }
> --
> 2.41.0
>

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