linux-kernel - Re: [RFC PATCH 03/86] Revert "ftrace: Use preemption model accessors for trace header printout"

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Message-ID: <20231107181057.334c815f@gandalf.local.home>
Date:   Tue, 7 Nov 2023 18:10:57 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
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Subject: Re: [RFC PATCH 03/86] Revert "ftrace: Use preemption model
 accessors for trace header printout"

On Tue,  7 Nov 2023 13:56:49 -0800
Ankur Arora <ankur.a.arora@...cle.com> wrote:

> This reverts commit 089c02ae2771a14af2928c59c56abfb9b885a8d7.

I rather not revert this.

If user space can decided between various version of preemption, then the
trace should reflect that. At least state what the preemption model was when
a trace started, or currently is.

That is, the model may not be "static" per boot. Anyway, the real change here should be:

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7b4b1fcd6f93..2553c4efca15 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2208,14 +2208,6 @@ static inline void cond_resched_rcu(void)
 #endif
 }
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
-
-extern bool preempt_model_none(void);
-extern bool preempt_model_voluntary(void);
-extern bool preempt_model_full(void);
-
-#else
-
 static inline bool preempt_model_none(void)
 {
 	return IS_ENABLED(CONFIG_PREEMPT_NONE);
@@ -2229,8 +2221,6 @@ static inline bool preempt_model_full(void)
 	return IS_ENABLED(CONFIG_PREEMPT);
 }
 
-#endif
-
 static inline bool preempt_model_rt(void)
 {
 	return IS_ENABLED(CONFIG_PREEMPT_RT);


Then this way we can decided to make it runtime dynamic, we don't need to
fiddle with the tracing code again.

-- Steve