linux-kernel - Re: [PATCH v8 01/24] tick/nohz: Move tick_nohz_full

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Date: Fri, 15 Dec 2023 21:31:42 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: James Morse <james.morse@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre
 <reinette.chatre@...el.com>, Ingo Molnar <mingo@...hat.com>, Borislav
 Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>, Babu Moger
 <Babu.Moger@....com>, James Morse <james.morse@....com>,
 shameerali.kolothum.thodi@...wei.com, D Scott Phillips OS
 <scott@...amperecomputing.com>, carl@...amperecomputing.com,
 lcherian@...vell.com, bobo.shaobowang@...wei.com,
 tan.shaopeng@...itsu.com, baolin.wang@...ux.alibaba.com, Jamie Iles
 <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
 peternewman@...gle.com, dfustini@...libre.com, amitsinght@...vell.com,
 Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v8 01/24] tick/nohz: Move tick_nohz_full_mask
 declaration outside the #ifdef

On Fri, Dec 15 2023 at 17:43, James Morse wrote:
> tick_nohz_full_mask lists the CPUs that are nohz_full. This is only
> needed when CONFIG_NO_HZ_FULL is defined. tick_nohz_full_cpu() allows
> a specific CPU to be tested against the mask, and evaluates to false
> when CONFIG_NO_HZ_FULL is not defined.
>
> The resctrl code needs to pick a CPU to run some work on, a new helper
> prefers housekeeping CPUs by examining the tick_nohz_full_mask. Hiding
> the declaration behind #ifdef CONFIG_NO_HZ_FULL forces all the users to
> be behind an ifdef too.
>
> Move the tick_nohz_full_mask declaration, this lets callers drop the
> ifdef, and guard access to tick_nohz_full_mask with IS_ENABLED() or
> something like tick_nohz_full_cpu().
>
> The definition does not need to be moved as any callers should be
> removed at compile time unless CONFIG_NO_HZ_FULL is defined.

I can pick that up separately, but I'm fine when it goes with the
resctrl lot. For that case:

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>