linux-kernel - Re: [PATCH] workqueue: Support RT workqueue

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Message-ID: <aPEQAqGOWOzzZl4Y@slm.duckdns.org>
Date: Thu, 16 Oct 2025 05:32:18 -1000
From: Tejun Heo <tj@...nel.org>
To: Xin Zhao <jackzxcui1989@....com>
Cc: jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Support RT workqueue

Hello,

On Thu, Oct 16, 2025 at 06:23:45PM +0800, Xin Zhao wrote:
> In a system with high real-time requirements, we have noticed that many
> high-priority tasks, such as kernel threads responsible for dispatching
> GPU tasks and receiving data sources, often experience latency spikes
> due to insufficient real-time execution of work.
> The kworker threads are shared globally based on the attributes of the
> workqueue (wq) and the parameters of queue_work_on. This means that
> regardless of whether you create a new wq or use an existing one, the
> kworker thread that processes the work does not exclusively run any
> specific work or work from a specific wq. While this design saves
> resources, it makes it difficult to ensure the real-time execution of
> work by modifying the priority of the kworker thread associated with a
> specific work in hard real-time scenarios. Additionally, if I manually
> set the real-time priority of the kworker while executing the work task
> and then adjust it back upon completion, the next time queue_work_on is
> called, the priority of the kworker thread will have reverted, making it
> impossible to ensure timely execution of these lower-priority threads.
> Moreover, frequent priority adjustments can incur additional overhead.
> Perhaps we could implement all logic related to hard real-time tasks
> using kernel threads, but I believe this workload is unnecessary. The
> existing workqueue mechanism in the system is well-structured and can
> guarantee that work executes in an orderly manner in concurrent scenarios
> by adjusting the max_active and WQ_ORDERED attributes. We only need to
> introduce a WQ_RT flag and add a small amount of code to meet the
> requirements of hard real-time workqueues.

For things that may need RT, please use kthread_work.

Thanks.

-- 
tejun