linux-kernel - Re: [PATCH v10 18/19] rv: Add documentation for rtapp monitor

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Message-ID: <20250630203456.5619393f@gandalf.local.home>
Date: Mon, 30 Jun 2025 20:34:56 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Nam Cao <namcao@...utronix.de>
Cc: Gabriele Monaco <gmonaco@...hat.com>,
 linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
 john.ogness@...utronix.de
Subject: Re: [PATCH v10 18/19] rv: Add documentation for rtapp monitor

On Tue, 10 Jun 2025 11:43:43 +0200
Nam Cao <namcao@...utronix.de> wrote:

> --- /dev/null
> +++ b/Documentation/trace/rv/monitor_rtapp.rst
> @@ -0,0 +1,116 @@
> +Real-time application monitors
> +==============================
> +
> +- Name: rtapp
> +- Type: container for multiple monitors
> +- Author: Nam Cao <namcao@...utronix.de>
> +
> +Description
> +-----------
> +
> +Real-time applications may have design flaws such that they experience unexpected latency and fail
> +to meet their time requirements. Often, these flaws follow a few patterns:
> +
> +  - Page faults: A real-time thread may access memory that does not have a mapped physical backing
> +    or must first be copied (such as for copy-on-write). Thus a page fault is raised and the kernel
> +    must first perform the expensive action. This causes significant delays to the real-time thread
> +  - Priority inversion: A real-time thread blocks waiting for a lower-priority thread. This causes
> +    the real-time thread to effectively take on the scheduling priority of the lower-priority
> +    thread. For example, the real-time thread needs to access a shared resource that is protected by
> +    a non-pi-mutex, but the mutex is currently owned by a non-real-time thread.
> +
> +The `rtapp` monitor detects these patterns. It aids developers to identify reasons for unexpected
> +latency with real-time applications. It is a container of multiple sub-monitors described in the
> +following sections.
> +

Again, please limit the documentation to 80 columns.

Thanks!

-- Steve