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

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Message-ID: <c77690ff-9f3d-4ab8-9443-b377134e90ca@nokia.com>
Date: Mon, 30 Jun 2025 15:59:17 +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 30/06/2025 15:25, Peter Zijlstra wrote:
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> 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?