linux-kernel - Re: [PATCH tip/core/rcu 15/24] rcu: Directly drive RCU_USER

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Date:	Wed, 13 May 2015 02:37:52 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 15/24] rcu: Directly drive RCU_USER_QS from
 Kconfig

On Tue, May 12, 2015 at 03:30:45PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> Currently, Kconfig will ask the user whether RCU_USER_QS should be set.
> This is silly because Kconfig already has all the information that it
> needs to set this parameter.  This commit therefore directly drives
> the value of RCU_USER_QS via NO_HZ_FULL's "select" statement.
> 
> Reported-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>

ACK. And we should remove it completely and use NO_HZ_FULL instead.
There won't seem to be more users.

> Reviewed-by: Pranith Kumar <bobby.prani@...il.com>
> ---
>  init/Kconfig | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 73db30a76afa..927210810189 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -529,9 +529,7 @@ config CONTEXT_TRACKING
>         bool
>  
>  config RCU_USER_QS
> -	bool "Consider userspace as in RCU extended quiescent state"
> -	depends on HAVE_CONTEXT_TRACKING && SMP
> -	select CONTEXT_TRACKING
> +	bool
>  	help
>  	  This option sets hooks on kernel / userspace boundaries and
>  	  puts RCU in extended quiescent state when the CPU runs in
> @@ -539,12 +537,6 @@ config RCU_USER_QS
>  	  excluded from the global RCU state machine and thus doesn't
>  	  try to keep the timer tick on for RCU.
>  
> -	  Unless you want to hack and help the development of the full
> -	  dynticks mode, you shouldn't enable this option.  It also
> -	  adds unnecessary overhead.
> -
> -	  If unsure say N
> -
>  config CONTEXT_TRACKING_FORCE
>  	bool "Force context tracking"
>  	depends on CONTEXT_TRACKING
> -- 
> 1.8.1.5
> 
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