linux-kernel - Re: [PATCH v2 1/5] tracing: Add support for creating hist trigger variables from literal

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Date:   Wed, 20 Oct 2021 08:55:23 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] tracing: Add support for creating hist trigger
 variables from literal

On Wed, Oct 20, 2021 at 8:32 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 19 Oct 2021 18:31:38 -0700
> Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> > @@ -89,6 +91,8 @@ typedef u64 (*hist_field_fn_t) (struct hist_field *field,
> >  #define HIST_FIELD_OPERANDS_MAX      2
> >  #define HIST_FIELDS_MAX              (TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
> >  #define HIST_ACTIONS_MAX     8
> > +#define HIST_CONST_MAX               4
>
> BTW, why is there a limit to the number of constants?

The motivation was to limit the number of hist_fields that can be
created for constants. These are also indirectly limited by the max
number of subexpressions (3) and the max number of vars/keys that can
be defined, so I don't feel strongly about keeping it.

Thanks,
Kalesh

>
> -- Steve
>
> > +#define HIST_CONST_DIGITS_MAX        21
> >