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

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Message-Id: <20251017082348.2998547-1-jackzxcui1989@163.com>
Date: Fri, 17 Oct 2025 16:23:48 +0800
From: Xin Zhao <jackzxcui1989@....com>
To: hch@...radead.org
Cc: jackzxcui1989@....com,
	jiangshanlai@...il.com,
	linux-kernel@...r.kernel.org,
	tj@...nel.org
Subject: Re: [PATCH] workqueue: Support RT workqueue

On Thu, 16 Oct 2025 23:26:35 -0700 Christoph Hellwig <hch@...radead.org> wrote:
> This seems to mis an actual user?  Did you accidentally only send
> patch 1 of a series?

It is a cross-module issue, I'm not quite sure if there is a better way to handle
this. Initially, I was thinking of proposing a patch to RT workqueue. If that gets
accepted, we could then use the newly created system_rt_wq in the patch to fix
the issues we found.
One of the issue is that where the DMA completion work task for UART data is not
processed in a timely manner, it leads to anomalies in handling IMU timestamps.
The proposed change could be to add a new function called tty_flip_buffer_push_rt,
which would be implemented as follows:

void tty_flip_buffer_push_rt(struct tty_port *port,
                             struct workqueue_struct *wq)
{
    struct tty_bufhead *buf = &port->buf;

    tty_flip_buffer_commit(buf->tail);
    queue_work(system_rt_wq, &buf->work);
}
EXPORT_SYMBOL(tty_flip_buffer_push_rt);

Our 8250 driver is implemented based on the TTY layer, but the tty_flip_buffer_push
function belongs to the TTY layer. Therefore, a possible patch for a user of the RT
workqueue could be the addition of the tty_flip_buffer_push_rt function to utilize
system_rt_wq. In addition, other changes, such as modifications to the GPU driver
code we maintain on our platform, can also use this RT workqueue, just pass WQ_RT
flag when creating the workqueue.

--
Xin Zhao