linux-kernel - Re: [PATCH] irq: add support for warning on long-running IRQ handlers

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Message-ID: <20250630132517.GM1613376@noisy.programming.kicks-ass.net>
Date: Mon, 30 Jun 2025 15:25:17 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Wladislav Wiebe <wladislav.wiebe@...ia.com>
Cc: anna-maria@...utronix.de, frederic@...nel.org, mingo@...nel.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	bigeasy@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: add support for warning on long-running IRQ handlers

On Mon, Jun 30, 2025 at 02:46:44PM +0200, Wladislav Wiebe wrote:
> Introduce a new option CONFIG_IRQ_LATENCY_WARN that enables warnings when
> IRQ handlers take an unusually long time to execute.
> 
> When triggered, the warning includes the CPU, IRQ number, handler address,
> name, and execution duration, for example:
> 
>   [CPU0] latency on IRQ[787:bad_irq_handler+0x1/0x34 [bad_irq]], took: 5 jiffies (~50 ms)
> 
> To keep runtime overhead minimal, this implementation uses a jiffies-based
> timing mechanism. While coarse, it is sufficient to detect problematic IRQs.

local_clock() was found to be excessively expensive?