linux-kernel - Re: [PATCH] watchdog: remove HARDLOCKUP_DETECTOR

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Message-ID: <CAP-5=fUs7WPQ1U-iXzZQDwa5Bm0Fg11Riw20AFnDDOScoY6BnA@mail.gmail.com>
Date: Mon, 15 Sep 2025 19:50:15 -0700
From: Ian Rogers <irogers@...gle.com>
To: Jinchao Wang <wangjinchao600@...il.com>
Cc: Doug Anderson <dianders@...omium.org>, Peter Zijlstra <peterz@...radead.org>, 
	Will Deacon <will@...nel.org>, Yunhui Cui <cuiyunhui@...edance.com>, akpm@...ux-foundation.org, 
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Subject: Re: [PATCH] watchdog: remove HARDLOCKUP_DETECTOR_PERF

On Mon, Sep 15, 2025 at 6:47 PM Jinchao Wang <wangjinchao600@...il.com> wrote:
> Should we support both modularization and changing the backend after
> boot, so that the user has the choice?

Having both together and then being able to choose one or the other
sounds like the ideal solution. An issue is that
/proc/sys/kernel/nmi_watchdog is used to dynamically enable/disable
both watchdogs and presumably renaming it for the buddy could cause
issues in user code.

There can be unexpected consequences of the buddy watchdog, as the NMI
perf event goes away there can be extra cost in setting up the first
event such as allocating buffers for the PMU. While enabling the NMI
watchdog to avoid this cost is kind of odd, I think users would be
glad of a workaround for what may be perceived as a regression.

Thanks,
Ian