linux-kernel - Re: [patch V2 1/1] Kconfig: Introduce CONFIG_PREEMPT

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Message-ID: <1563477813.12300.2.camel@kernel.org>
Date:   Thu, 18 Jul 2019 14:23:33 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Christoph Hellwig <hch@....de>, Tejun Heo <tj@...nel.org>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <clark.williams@...il.com>,
        Julia Cartwright <julia@...com>,
        Marc Zyngier <marc.zyngier@....com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Gratian Crisan <gratian.crisan@...com>
Subject: Re: [patch V2 1/1] Kconfig: Introduce CONFIG_PREEMPT_RT

Hi,

On Wed, 2019-07-17 at 22:01 +0200, Thomas Gleixner wrote:
> Add a new entry to the preemption menu which enables the real-time
> support
> for the kernel. The choice is only enabled when an architecture
> supports
> it.
> 
> It selects PREEMPT as the RT features depend on it. To achieve that
> the
> existing PREEMPT choice is renamed to PREEMPT_LL which select PREEMPT
> as
> well.
> 
> No functional change.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Paul E. McKenney <paulmck@...ux.ibm.com>
> Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> Acked-by: Clark Williams <williams@...hat.com>
> Acked-by: Daniel Bristot de Oliveira <bristot@...hat.com>
> Acked-by: Frederic Weisbecker <frederic@...nel.org>
> Acked-by: Ingo Molnar <mingo@...nel.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Marc Zyngier <marc.zyngier@....com>
> Acked-by: Daniel Wagner <wagi@...om.org>
> ---

As one of the stable-rt maintainers, I'd obviously be very happy to see
this finally go in.  :-)

And will be happy to do what I can to help with the remaining 311...

Acked-by: Tom Zanussi <tom.zanussi@...ux.intel.com>


> V2: Fix typos in help text, collect acks
> ---
>  arch/Kconfig           |    3 +++
>  kernel/Kconfig.preempt |   25 +++++++++++++++++++++++--
>  2 files changed, 26 insertions(+), 2 deletions(-)
> 
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -809,6 +809,9 @@ config ARCH_NO_COHERENT_DMA_MMAP
>  config ARCH_NO_PREEMPT
>  	bool
>  
> +config ARCH_SUPPORTS_RT
> +	bool
> +
>  config CPU_NO_EFFICIENT_FFS
>  	def_bool n
>  
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -35,10 +35,10 @@ config PREEMPT_VOLUNTARY
>  
>  	  Select this if you are building a kernel for a desktop
> system.
>  
> -config PREEMPT
> +config PREEMPT_LL
>  	bool "Preemptible Kernel (Low-Latency Desktop)"
>  	depends on !ARCH_NO_PREEMPT
> -	select PREEMPT_COUNT
> +	select PREEMPT
>  	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
>  	help
>  	  This option reduces the latency of the kernel by making
> @@ -55,7 +55,28 @@ config PREEMPT
>  	  embedded system with latency requirements in the
> milliseconds
>  	  range.
>  
> +config PREEMPT_RT
> +	bool "Fully Preemptible Kernel (Real-Time)"
> +	depends on EXPERT && ARCH_SUPPORTS_RT
> +	select PREEMPT
> +	help
> +	  This option turns the kernel into a real-time kernel by
> replacing
> +	  various locking primitives (spinlocks, rwlocks, etc.) with
> +	  preemptible priority-inheritance aware variants, enforcing
> +	  interrupt threading and introducing mechanisms to break up
> long
> +	  non-preemptible sections. This makes the kernel, except
> for very
> +	  low level and critical code pathes (entry code, scheduler,
> low
> +	  level interrupt handling) fully preemptible and brings
> most
> +	  execution contexts under scheduler control.
> +
> +	  Select this if you are building a kernel for systems which
> +	  require real-time guarantees.
> +
>  endchoice
>  
>  config PREEMPT_COUNT
>         bool
> +
> +config PREEMPT
> +       bool
> +       select PREEMPT_COUNT