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

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Message-ID: <9ae77072-fb55-4ea3-bf9d-60db96d6a85c@nokia.com>
Date: Wed, 2 Jul 2025 11:14:57 +0200
From: Wladislav Wiebe <wladislav.wiebe@...ia.com>
To: Peter Zijlstra <peterz@...radead.org>
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 02/07/2025 11:06, Peter Zijlstra wrote:
> 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.

I plan to refactor it to cover it with local_clock() and to avoid using Kconfig knobs as based on Thomas Gleixner comments. Thanks for the feedback. - W.W.