linux-kernel - Re: [PATCH 29/30] Documentation: tracing: add TIF_NEED_RESCHED

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Message-ID: <87bk89e72r.fsf@oracle.com>
Date: Wed, 21 Feb 2024 15:22:20 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org,
        torvalds@...ux-foundation.org, paulmck@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, willy@...radead.org,
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        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan
 Corbet <corbet@....net>
Subject: Re: [PATCH 29/30] Documentation: tracing: add TIF_NEED_RESCHED_LAZY


Steven Rostedt <rostedt@...dmis.org> writes:

> On Mon, 12 Feb 2024 21:55:53 -0800
> Ankur Arora <ankur.a.arora@...cle.com> wrote:
>
>> Document various combinations of resched flags.
>>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> Cc: Jonathan Corbet <corbet@....net>
>> Originally-by: Thomas Gleixner <tglx@...utronix.de>
>> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
>> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
>> ---
>>  Documentation/trace/ftrace.rst | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
>> index 7e7b8ec17934..7f20c0bae009 100644
>> --- a/Documentation/trace/ftrace.rst
>> +++ b/Documentation/trace/ftrace.rst
>> @@ -1036,8 +1036,12 @@ explains which is which.
>>  		be printed here.
>>
>>    need-resched:
>> -	- 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
>> +	- 'B' all three, TIF_NEED_RESCHED, TIF_NEED_RESCHED_LAZY and PREEMPT_NEED_RESCHED are set,
>> +	- 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED are set,
>> +	- 'L' both TIF_NEED_RESCHED_LAZY and PREEMPT_NEED_RESCHED are set,
>> +	- 'b' both TIF_NEED_RESCHED and TIF_NEED_RESCHED_LAZY are set,
>>  	- 'n' only TIF_NEED_RESCHED is set,
>> +	- 'l' only TIF_NEED_RESCHED_LAZY is set,
>>  	- 'p' only PREEMPT_NEED_RESCHED is set,
>>  	- '.' otherwise.
>>
>
> I wonder if we should also add this information in /sys/kernel/tracing/README
> so that it is easier to find on a machine.

Yeah, there is a problem with the discovery. Seems a little out of place
in tracing/README though.

How about something like this? Though this isn't really a model of clarity.

    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -4292,7 +4292,7 @@ static void print_lat_help_header(struct seq_file *m)
    {
            seq_puts(m, "#                    _------=> CPU#            \n"
                    "#                   / _-----=> irqs-off/BH-disabled\n"
    -                   "#                  | / _----=> need-resched    \n"
    +                   "#                  | / _----=> need-resched  [ l: lazy, n: now, p: preempt, b: l|n, L: l|p, N: n|p, B: l|n|p ]\n"
                    "#                  || / _---=> hardirq/softirq \n"
                    "#                  ||| / _--=> preempt-depth   \n"
                    "#                  |||| / _-=> migrate-disable \n"


Also, haven't looked at trace-cmd. Anything I should be sending a patch
out for?

Thanks

--
ankur