linux-kernel - Re: [PATCH 3/4] nohz: add tick_nohz_full_clear

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Date:	Mon, 30 Mar 2015 12:20:17 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	<linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Kevin Hilman <khilman@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 3/4] nohz: add tick_nohz_full_clear_cpus() API

I wanted to ping the patch below again, since I haven't heard any
feedback.

I note that Rik van Riel's change posted this weekend offers similar
functionality for userspace.  My change offers a convenient API
for, e.g., kernel drivers setting up default irq balancing.

https://lkml.org/lkml/2015/3/28/94

Although it would be possible to do the same thing by iterating over
the existing tick_nohz_full_cpu() API, that seems kind of silly.

An alternate API would be one that just returned the full no_hz
cpumask to kernel callers; I'd be happy with that as well, but my
instinct was to make the API as narrow as possible to start with.

Comments?

On 03/24/2015 03:21 PM, cmetcalf@...hip.com wrote:
> From: Chris Metcalf <cmetcalf@...hip.com>
>
> This is useful, for example, to modify a cpumask to avoid the
> nohz cores so that interrupts aren't sent to them.
>
> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> ---
> Motivated by patch 4/4 in this series.
>
>   include/linux/tick.h | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index 9c085dc12ae9..d53ad4892a39 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -186,6 +186,12 @@ static inline bool tick_nohz_full_cpu(int cpu)
>   	return cpumask_test_cpu(cpu, tick_nohz_full_mask);
>   }
>   
> +static inline void tick_nohz_full_clear_cpus(struct cpumask *mask)
> +{
> +	if (tick_nohz_full_enabled())
> +		cpumask_andnot(mask, mask, tick_nohz_full_mask);
> +}
> +
>   extern void __tick_nohz_full_check(void);
>   extern void tick_nohz_full_kick(void);
>   extern void tick_nohz_full_kick_cpu(int cpu);
> @@ -194,6 +200,7 @@ extern void __tick_nohz_task_switch(struct task_struct *tsk);
>   #else
>   static inline bool tick_nohz_full_enabled(void) { return false; }
>   static inline bool tick_nohz_full_cpu(int cpu) { return false; }
> +static inline void tick_nohz_full_clear_cpus(struct cpumask *mask) { }
>   static inline void __tick_nohz_full_check(void) { }
>   static inline void tick_nohz_full_kick_cpu(int cpu) { }
>   static inline void tick_nohz_full_kick(void) { }

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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