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From: Mike Galbraith <efault@gmx.de>
To: Valentin Schneider <valentin.schneider@arm.com>,
	linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH] sched: Tweak default dynamic preempt mode selection
Date: Sat, 06 Nov 2021 05:40:30 +0100	[thread overview]
Message-ID: <ff53a94401f8d6abe0303ee381f86bfb475ad354.camel@gmx.de> (raw)
In-Reply-To: <20211105104035.3112162-1-valentin.schneider@arm.com>

On Fri, 2021-11-05 at 10:40 +0000, Valentin Schneider wrote:
> Commit c597bfddc9e9 ("sched: Provide Kconfig support for default dynamic
> preempt mode") changed the selectable config names for the preemption
> model. This means a config file must now select
>
>   CONFIG_PREEMPT_BEHAVIOUR=y
>
> rather than
>
>   CONFIG_PREEMPT=y
>
> to get a preemptible kernel. This means all arch config files need to be
> updated - right now arm64 defconfig selects CONFIG_PREEMPT=y but ends up
> with CONFIG_PREEMPT_NONE_BEHAVIOUR=y.
>
> Instead, have CONFIG_*PREEMPT be the selectable configs again, and make
> them select their _BEHAVIOUR equivalent if CONFIG_PREEMPT_DYNAMIC is set.


Is there any way to get to PREEMPT_RT in the first selection again as
well?  I had created a behavior entry for RT (below) and inverted the
dependency to make it appear in the initial selection again, but that's
clearly not gonna fly.

Starting with a 5.15 config, to select RT you currently must first
select a model you don't want, then reject PREEMPT_DYNAMIC and you'll
be offered the full menu of models immediately. With your patch added,
that became worse.  After rejecting PREEMPT_DYNAMIC, I had to go
through new 5.15+ options before finally being offered the full menu.

	-Mike

--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -56,10 +56,10 @@ config PREEMPT_BEHAVIOUR
 	  embedded system with latency requirements in the
milliseconds
 	  range.

-config PREEMPT_RT
+config PREEMPT_RT_BEHAVIOR
 	bool "Fully Preemptible Kernel (Real-Time)"
-	depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC
-	select PREEMPTION
+	depends on EXPERT && ARCH_SUPPORTS_RT
+	select PREEMPT_RT
 	help
 	  This option turns the kernel into a real-time kernel by
replacing
 	  various locking primitives (spinlocks, rwlocks, etc.) with
@@ -86,6 +86,10 @@ config PREEMPT
 	select PREEMPTION
 	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK

+config PREEMPT_RT
+	bool
+	select PREEMPTION
+
 config PREEMPT_COUNT
        bool

@@ -101,7 +105,7 @@ config PREEMPT_LAZY

 config PREEMPT_DYNAMIC
 	bool "Preemption behaviour defined on boot"
-	depends on HAVE_PREEMPT_DYNAMIC
+	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
 	select PREEMPT
 	default y
 	help




  reply	other threads:[~2021-11-06  4:41 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-05 10:40 [PATCH] sched: Tweak default dynamic preempt mode selection Valentin Schneider
2021-11-06  4:40 ` Mike Galbraith [this message]
2021-11-08 11:17   ` Valentin Schneider
2021-11-08 12:27     ` Mike Galbraith
2021-11-08 15:21       ` Valentin Schneider
2021-11-09  5:30         ` Mike Galbraith
2021-11-09  9:52           ` Valentin Schneider
2021-11-09 11:00             ` Mike Galbraith
2021-11-09 12:19               ` Valentin Schneider
2021-11-09 13:31                 ` Mike Galbraith
2021-11-06  5:05 ` kernel test robot
2021-11-06  5:05   ` kernel test robot
2021-11-08 12:00   ` Valentin Schneider
2021-11-08 12:00     ` Valentin Schneider
2021-11-06  5:33 ` kernel test robot
2021-11-06  5:33   ` kernel test robot
2021-11-06  7:58 ` kernel test robot
2021-11-06  7:58   ` kernel test robot
2021-11-09 10:25 ` Frederic Weisbecker
2021-11-10  0:03   ` Valentin Schneider
2021-11-10  5:44     ` Mike Galbraith

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