linux-kernel - Re: [PATCH] tracing/sched: add 'next_policy' to trace_sched

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Message-ID: <20250822100209.7b1c5acf@gandalf.local.home>
Date: Fri, 22 Aug 2025 10:02:09 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Xiang Gao <gxxa03070307@...il.com>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com, andrii@...nel.org,
 mingo@...nel.org, oleg@...hat.com, akpm@...ux-foundation.org,
 gmonaco@...hat.com, ricardo.neri-calderon@...ux.intel.com,
 libo.chen@...cle.com, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, gaoxiang17 <gaoxiang17@...omi.com>
Subject: Re: [PATCH] tracing/sched: add 'next_policy' to trace_sched_switch

On Fri, 22 Aug 2025 18:51:13 +0800
Xiang Gao <gxxa03070307@...il.com> wrote:

> From: gaoxiang17 <gaoxiang17@...omi.com>
> 
> Sometimes, when analyzing some real-time process issues, it is necessary to know the sched policy.
> 
> Show up in the trace as:
> 
>       113.457176: sched_switch: prev_comm=kcompactd0 prev_pid=30 prev_prio=120 prev_state=S ==> next_comm=kworker/u4:1 next_pid=27 next_prio=120 next_policy=0
>       113.457282: sched_switch: prev_comm=kworker/u4:1 prev_pid=27 prev_prio=120 prev_state=I ==> next_comm=swapper/0 next_pid=0 next_prio=120 next_policy=0
>       113.461166: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/u4:1 next_pid=27 next_prio=120 next_policy=0
> 
> Signed-off-by: gaoxiang17 <gaoxiang17@...omi.com>
> ---
>  include/trace/events/sched.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 7b2645b50e78..b416b7bafee4 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -234,6 +234,7 @@ TRACE_EVENT(sched_switch,
>  		__array(	char,	next_comm,	TASK_COMM_LEN	)
>  		__field(	pid_t,	next_pid			)
>  		__field(	int,	next_prio			)
> +		__field(	unsigned int,	next_policy	)
>  	),
>  
>  	TP_fast_assign(
> @@ -244,10 +245,11 @@ TRACE_EVENT(sched_switch,
>  		memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
>  		__entry->next_pid	= next->pid;
>  		__entry->next_prio	= next->prio;
> +		__entry->next_policy	= next->policy;
>  		/* XXX SCHED_DEADLINE */
>  	),
>  
> -	TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d",
> +	TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d next_policy=%u",
>  		__entry->prev_comm, __entry->prev_pid, __entry->prev_prio,
>  
>  		(__entry->prev_state & (TASK_REPORT_MAX - 1)) ?
> @@ -263,7 +265,7 @@ TRACE_EVENT(sched_switch,
>  		  "R",
>  
>  		__entry->prev_state & TASK_REPORT_MAX ? "+" : "",
> -		__entry->next_comm, __entry->next_pid, __entry->next_prio)
> +		__entry->next_comm, __entry->next_pid, __entry->next_prio, __entry->next_policy)


I'm fine with this change, but I'm not sure how Peter feels about updating
scheduler tracepoints. That said, why not show the policy name?

	TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d next_policy=%s",
	[..]
		__entry->next_comm, __entry->next_pid, __entry->next_prio,
		__print_symbolic(__entry->next_policy,
			{ SCHED_NORMAL,		"normal" },
			{ SCHED_FIFO,		"FIFO" },
			{ SCHED_RR,		"RR" },
			{ SCHED_BATCH,		"batch" },
			{ SCHED_IDLE,		"idle" },
			{ SCHED_DEADLINE,	"deadline" },
			{ SCHED_EXT,		"sched_ext"}))

-- Steve






>  );
>  
>  /*