linux-kernel - Re: [PATCH tip/core/rcu 4/7] rcu: Unify boost and kthread priorities

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Message-ID: <20141029110146.GA3337@twins.programming.kicks-ass.net>
Date:	Wed, 29 Oct 2014 12:01:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
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, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
	Clark Williams <clark.williams@...il.com>
Subject: Re: [PATCH tip/core/rcu 4/7] rcu: Unify boost and kthread priorities

On Tue, Oct 28, 2014 at 03:22:59PM -0700, Paul E. McKenney wrote:
> From: Clark Williams <clark.williams@...il.com>
> 
> Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> threads (rcub/n).
> 
> Also, create the module_parameter rcutree.kthread_prio to be used on
> the kernel command line at boot to set a new value (rcutree.kthread_prio=N).
> 
> Signed-off-by: Clark Williams <clark.williams@...il.com>
> [ paulmck: Ported to rcu/dev, applied Paul Bolle feedback. ]
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  Documentation/kernel-parameters.txt                |  6 ++++++
>  init/Kconfig                                       | 23 +++++++++++-----------
>  kernel/rcu/tree_plugin.h                           | 20 +++++++++----------
>  .../selftests/rcutorture/configs/rcu/TREE03        |  2 +-
>  .../selftests/rcutorture/doc/TREE_RCU-kconfig.txt  |  4 ++--
>  5 files changed, 31 insertions(+), 24 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 7dbe5ec9d9cd..7d3b3328bf5c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2922,6 +2922,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			quiescent states.  Units are jiffies, minimum
>  			value is one, and maximum value is HZ.
>  
> +	rcutree.kthread_prio= 	 [KNL,BOOT]
> +			Set the SCHED_FIFO priority of the RCU
> +			per-CPU kthreads (rcuc/N). This value is also
> +			used for the priority of the RCU boost threads
> +			(rcub/N). Valid values are 1-99.
> +

It would maybe be useful to mention the default?

Also, should we look at running this stuff as deadline in order to
provide interference guarantees etc.. ?
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