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

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Message-ID: <c9706a35-4a61-df51-2c70-d4bab62f9eab@intel.com>
Date:   Thu, 24 Aug 2023 17:43:59 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....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 James,

On 8/24/2023 9:55 AM, James Morse wrote:
> 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.

At the moment this change is buried within a pile of resctrl
changes so we need to make sure that folks are not surprised by this
thinking we are trying to sneak it in. Please note that
CC is currently missing Frederic Weisbecker.
I wonder if it may help to change cover letter to be something like
"x86/resctrl and tick/nohz: Monitor ..." Just an idea.

Reinette