linux-kernel - Re: [PATCH v2 1/3] tracing: Replace TRACE_FLAG_IRQS

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Message-ID: <20241022031418.12154e63@rorschach.local.home>
Date: Tue, 22 Oct 2024 03:14:18 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org, Peter
 Zijlstra <peterz@...radead.org>, tglx@...utronix.de, mingo@...nel.org,
 juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, ankur.a.arora@...cle.com, efault@....de, Masami
 Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v2 1/3] tracing: Replace TRACE_FLAG_IRQS_NOSUPPORT with
 its config option.

On Mon, 21 Oct 2024 17:08:40 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The TRACE_FLAG_IRQS_NOSUPPORT flag is used by tracing_gen_ctx.*() to
> signal that CONFIG_TRACE_IRQFLAGS_SUPPORT is not enabled and tracing IRQ
> flags is not supported.
> 
> This could be replaced by using the 0 as flags and then deducting that
> there is no IRQFLAGS_SUPPORT based on the config option. The downside is
> that without CONFIG_TRACE_IRQFLAGS_SUPPORT we can not distinguish
> between no-IRQ passed flags and callers which passed 0. On the upside we
> have room for one additional flags which could be used for LAZY_PREEMPTION.
> 
> Remove TRACE_FLAG_IRQS_NOSUPPORT and set it flags are 0 and
> CONFIG_TRACE_IRQFLAGS_SUPPORT is not set.

We could also add that we have:

#
# Minimum requirements an architecture has to meet for us to
# be able to offer generic tracing facilities:
#
config TRACING_SUPPORT
        bool
        depends on TRACE_IRQFLAGS_SUPPORT
        depends on STACKTRACE_SUPPORT
        default y

So this can't even be built without TRACE_IRQFLAGS_SUPPORT!

> 
> [bigeasy: Commit descrption.]
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  include/linux/trace_events.h |    7 +++----
>  kernel/trace/trace_output.c  |    2 +-
>  2 files changed, 4 insertions(+), 5 deletions(-)
> 
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -184,8 +184,7 @@ unsigned int tracing_gen_ctx_irq_test(un
>  
>  enum trace_flag_type {
>  	TRACE_FLAG_IRQS_OFF		= 0x01,
> -	TRACE_FLAG_IRQS_NOSUPPORT	= 0x02,
> -	TRACE_FLAG_NEED_RESCHED		= 0x04,
> +	TRACE_FLAG_NEED_RESCHED		= 0x02,

These flags are user visible (I probably should move them into uapi).
They are parsed by libtraceevent.

Please just remove NOSUPPORT and do not touch NEED_RESCHED.


>  	TRACE_FLAG_HARDIRQ		= 0x08,
>  	TRACE_FLAG_SOFTIRQ		= 0x10,
>  	TRACE_FLAG_PREEMPT_RESCHED	= 0x20,
> @@ -211,11 +210,11 @@ static inline unsigned int tracing_gen_c
>  
>  static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
>  {
> -	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
> +	return tracing_gen_ctx_irq_test(0);
>  }
>  static inline unsigned int tracing_gen_ctx(void)
>  {
> -	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
> +	return tracing_gen_ctx_irq_test(0);
>  }
>  #endif
>  
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -460,7 +460,7 @@ int trace_print_lat_fmt(struct trace_seq
>  		(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
>  		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
>  		bh_off ? 'b' :
> -		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
> +		!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :

Probably can even remove this check.

-- Steve

>  		'.';
>  
>  	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |