linux-kernel - Re: [PATCH 33/33] doc: Add housekeeping documentation

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Message-ID: <aVVAfb2eaeyd7l-h@localhost.localdomain>
Date: Wed, 31 Dec 2025 16:25:49 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <llong@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Chen Ridong <chenridong@...wei.com>,
	Danilo Krummrich <dakr@...nel.org>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Gabriele Monaco <gmonaco@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
	Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
	Paolo Abeni <pabeni@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, Phil Auld <pauld@...hat.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Simon Horman <horms@...nel.org>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
	cgroups@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-block@...r.kernel.org, linux-mm@...ck.org,
	linux-pci@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 33/33] doc: Add housekeeping documentation

Le Fri, Dec 26, 2025 at 07:39:28PM -0500, Waiman Long a écrit :
> On 12/24/25 8:45 AM, Frederic Weisbecker wrote:
> > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > ---
> >   Documentation/core-api/housekeeping.rst | 111 ++++++++++++++++++++++++
> >   Documentation/core-api/index.rst        |   1 +
> >   2 files changed, 112 insertions(+)
> >   create mode 100644 Documentation/core-api/housekeeping.rst
> > 
> > diff --git a/Documentation/core-api/housekeeping.rst b/Documentation/core-api/housekeeping.rst
> > new file mode 100644
> > index 000000000000..e5417302774c
> > --- /dev/null
> > +++ b/Documentation/core-api/housekeeping.rst
> > @@ -0,0 +1,111 @@
> > +======================================
> > +Housekeeping
> > +======================================
> > +
> > +
> > +CPU Isolation moves away kernel work that may otherwise run on any CPU.
> > +The purpose of its related features is to reduce the OS jitter that some
> > +extreme workloads can't stand, such as in some DPDK usecases.
> Nit: "usecases" => "use cases"

Are you sure? I'm not a native speaker but at least the kernel
has established its use:

$ git grep usecase | wc -l
517

> > +
> > +The kernel work moved away by CPU isolation is commonly described as
> > +"housekeeping" because it includes ground work that performs cleanups,
> > +statistics maintainance and actions relying on them, memory release,
> > +various deferrals etc...
> > +
> > +Sometimes housekeeping is just some unbound work (unbound workqueues,
> > +unbound timers, ...) that gets easily assigned to non-isolated CPUs.
> > +But sometimes housekeeping is tied to a specific CPU and requires
> > +elaborated tricks to be offloaded to non-isolated CPUs (RCU_NOCB, remote
> > +scheduler tick, etc...).
> > +
> > +Thus, a housekeeping CPU can be considered as the reverse of an isolated
> > +CPU. It is simply a CPU that can execute housekeeping work. There must
> > +always be at least one online housekeeping CPU at any time. The CPUs that
> > +are not	isolated are automatically assigned as housekeeping.
> Nit: extra white spaces between "not" and "isolated".

Somehow it has disappeared in my tree, some Brunaidh must have fixed
that while I was sleeping. That's nice!

> > diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
> > index 5eb0fbbbc323..79fe7735692e 100644
> > --- a/Documentation/core-api/index.rst
> > +++ b/Documentation/core-api/index.rst
> > @@ -25,6 +25,7 @@ it.
> >      symbol-namespaces
> >      asm-annotations
> >      real-time/index
> > +   housekeeping.rst
> >   Data structures and low-level utilities
> >   =======================================
> Acked-by: Waiman Long <longman@...hat.com>

Thanks! 

-- 
Frederic Weisbecker
SUSE Labs