linux-kernel - Re: [PATCH v3] tracing: Record task flag NEED_RESCHED

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Message-ID: <20241122143742.038c77fa@gandalf.local.home>
Date: Fri, 22 Nov 2024 14:37:42 -0500
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 v3] tracing: Record task flag NEED_RESCHED_LAZY.

On Fri, 22 Nov 2024 18:32:01 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The scheduler added NEED_RESCHED_LAZY scheduling. Record this state as
> part of trace flags and expose it in the need_resched field.
> 
> Record and expose NEED_RESCHED_LAZY.
> 
> [bigeasy: Commit description, documentation bits.]
> 
> Reviewed-by: Ankur Arora <ankur.a.arora@...cle.com>
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> v2…v3:
>   - Use 0x02 for TRACE_FLAG_NEED_RESCHED_LAZY which is the freshly
>     created gap.
> 
>  Documentation/trace/ftrace.rst |  4 ++++
>  include/linux/trace_events.h   |  1 +
>  kernel/trace/trace.c           |  2 ++
>  kernel/trace/trace_output.c    | 14 +++++++++++++-
>  4 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
> index 74d5bd801b1a8..16892b844108c 100644
> --- a/Documentation/trace/ftrace.rst
> +++ b/Documentation/trace/ftrace.rst
> @@ -1033,9 +1033,13 @@ explains which is which.
>    irqs-off: 'd' interrupts are disabled. '.' otherwise.
>  
>    need-resched:
> +	- 'B' all, TIF_NEED_RESCHED, PREEMPT_NEED_RESCHED and TIF_RESCHED_LAZY is set,
>  	- 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
>  	- 'n' only TIF_NEED_RESCHED is set,
>  	- 'p' only PREEMPT_NEED_RESCHED is set,

> +	- 'L' borg PREEMPT_NEED_RESCHED and TIF_RESCHED_LAZY is set,
> +	- 'b' borg TIF_NEED_RESCHED and TIF_RESCHED_LAZY is set,

   Is resistance futile?

I can switch it over to "both" if that's what you meant.

-- Steve

> +	- 'l' only TIF_RESCHED_LAZY is set
>  	- '.' otherwise.
>  
>    hardirq/softirq:
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 016b29a56c875..2a5df5b62cfc7 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -184,6 +184,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status);
>  
>  enum trace_flag_type {
>  	TRACE_FLAG_IRQS_OFF		= 0x01,
> +	TRACE_FLAG_NEED_RESCHED_LAZY	= 0x02,
>  	TRACE_FLAG_NEED_RESCHED		= 0x04,
>  	TRACE_FLAG_HARDIRQ		= 0x08,
>  	TRACE_FLAG_SOFTIRQ		= 0x10,
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 3ef047ed97055..be62f0ea1814d 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2552,6 +2552,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
>  		trace_flags |= TRACE_FLAG_NEED_RESCHED;
>  	if (test_preempt_need_resched())
>  		trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
> +	if (IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY) && tif_test_bit(TIF_NEED_RESCHED_LAZY))
> +		trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY;
>  	return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) |
>  		(min_t(unsigned int, migration_disable_value(), 0xf)) << 4;
>  }
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index e08aee34ef63d..da748b7cbc4d5 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -462,17 +462,29 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
>  		bh_off ? 'b' :
>  		'.';
>  
> -	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
> +	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY |
>  				TRACE_FLAG_PREEMPT_RESCHED)) {
> +	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
> +		need_resched = 'B';
> +		break;
>  	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
>  		need_resched = 'N';
>  		break;
> +	case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
> +		need_resched = 'L';
> +		break;
> +	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY:
> +		need_resched = 'b';
> +		break;
>  	case TRACE_FLAG_NEED_RESCHED:
>  		need_resched = 'n';
>  		break;
>  	case TRACE_FLAG_PREEMPT_RESCHED:
>  		need_resched = 'p';
>  		break;
> +	case TRACE_FLAG_NEED_RESCHED_LAZY:
> +		need_resched = 'l';
> +		break;
>  	default:
>  		need_resched = '.';
>  		break;