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

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Message-ID: <20250702090614.GP1613200@noisy.programming.kicks-ass.net>
Date: Wed, 2 Jul 2025 11:06:14 +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 03:59:17PM +0200, Wladislav Wiebe wrote:
> 
> On 30/06/2025 15:25, Peter Zijlstra wrote:
> > CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> >
> >
> >
> > 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?
> 
> Perhaps not excessively expensive, but jiffies is the lowest-overhead option here, isn't it?

Yeah, but since it varies in length and even the shortest (1ms) might be
too long for some, it is of very limited use.