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

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Date: Mon, 22 Jan 2024 18:05:21 +0000
From: James Morse <james.morse@....com>
To: Thomas Gleixner <tglx@...utronix.de>, 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>, 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

Hi Thomas,

On 15/12/2023 20:31, Thomas Gleixner wrote:
> 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>


Thanks!

James