linux-kernel - Re: [PATCH 4/5] perf record: Allow to specify max stack depth of fp callchain

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Date:   Wed, 1 Jun 2022 23:29:42 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH 4/5] perf record: Allow to specify max stack depth of fp callchain

On Tue, May 31, 2022 at 11:58 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Currently it has no interface to specify the max stack depth for perf
> record.  Extend the command line parameter to accept a number after
> 'fp' to specify the depth like '--call-graph fp,32'.

It is valid to have call-graph=fp as a modifier on an event. To
support a depth with that we couldn't use ',' as it is already the
separator between modifiers. For consistency maybe a different
separator should be used here?

Thanks,
Ian

>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/Documentation/perf-record.txt |  5 +++++
>  tools/perf/util/callchain.c              | 18 ++++++++++++------
>  2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index b4e9ef7edfef..d2759e2ccf9e 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -275,6 +275,11 @@ OPTIONS
>         User can change the size by passing the size after comma like
>         "--call-graph dwarf,4096".
>
> +       When "fp" recording is used, perf tries to save stack enties
> +       up to the number specified in sysctl.kernel.perf_event_max_stack
> +       by default.  User can change the number by passing it after comma
> +       like "--call-graph fp,32".
> +
>  -q::
>  --quiet::
>         Don't print any message, useful for scripting.
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 5c27a4b2e7a7..7e663673f79f 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -31,6 +31,7 @@
>  #include "callchain.h"
>  #include "branch.h"
>  #include "symbol.h"
> +#include "util.h"
>  #include "../perf.h"
>
>  #define CALLCHAIN_PARAM_DEFAULT                        \
> @@ -266,12 +267,17 @@ int parse_callchain_record(const char *arg, struct callchain_param *param)
>         do {
>                 /* Framepointer style */
>                 if (!strncmp(name, "fp", sizeof("fp"))) {
> -                       if (!strtok_r(NULL, ",", &saveptr)) {
> -                               param->record_mode = CALLCHAIN_FP;
> -                               ret = 0;
> -                       } else
> -                               pr_err("callchain: No more arguments "
> -                                      "needed for --call-graph fp\n");
> +                       ret = 0;
> +                       param->record_mode = CALLCHAIN_FP;
> +
> +                       tok = strtok_r(NULL, ",", &saveptr);
> +                       if (tok) {
> +                               unsigned long size;
> +
> +                               size = strtoul(tok, &name, 0);
> +                               if (size < (unsigned) sysctl__max_stack())
> +                                       param->max_stack = size;
> +                       }
>                         break;
>
>                 /* Dwarf style */
> --
> 2.36.1.255.ge46751e96f-goog
>