linux-kernel - Re: [PATCH v5 10/24] tick/nohz: Move tick_nohz_full

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Message-ID: <fb244874-da8f-ac6f-511f-92861a340abe@arm.com>
Date:   Thu, 24 Aug 2023 17:55:11 +0100
From:   James Morse <james.morse@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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,
        xingxin.hx@...nanolis.org, baolin.wang@...ux.alibaba.com,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
        dfustini@...libre.com
Subject: Re: [PATCH v5 10/24] tick/nohz: Move tick_nohz_full_mask declaration
 outside the #ifdef

Hi Reinette,

On 09/08/2023 23:34, Reinette Chatre wrote:
> On 7/28/2023 9:42 AM, 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.
>>
>> Signed-off-by: James Morse <james.morse@....com>
>> ---
>>  include/linux/tick.h | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> This is outside of the resctrl area. What is the upstreaming
> plan for this patch?

Once you're happy with the rest of it - we can give the other folk on CC a poke.
I'd assume changes to this file also go via tip. It would just need an ack from the
relevant person.


Thanks,

James