linux-kernel - Re: [PATCH v3 0/2] Reduce CPU consumption after panic

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Message-ID: <94faa778-38d5-4ea5-aa0d-9259b56999a4@vt.edu>
Date: Tue, 29 Apr 2025 15:52:05 -0500
From: Carlos Bilbao <bilbao@...edu>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, carlos.bilbao@...nel.org,
 tglx@...utronix.de, seanjc@...gle.com, jan.glauber@...il.com,
 pmladek@...e.com, jani.nikula@...el.com, linux-kernel@...r.kernel.org,
 gregkh@...uxfoundation.org, takakura@...inux.co.jp,
 john.ogness@...utronix.de, x86@...nel.org
Subject: Re: [PATCH v3 0/2] Reduce CPU consumption after panic

Hello,

On 4/29/25 17:10, Peter Zijlstra wrote:
> On Tue, Apr 29, 2025 at 03:32:56PM -0500, Carlos Bilbao wrote:
> 
>> Yes, the machine is effectively dead, but as things stand today,
>> it's still drawing resources unnecessarily.
>>
>> Who cares? An example, as mentioned in the cover letter, is Linux running
> 
> Ah, see, I didn't have no cover letter, only akpm's reply.
> 
>> in VMs. Imagine a scenario where customers are billed based on CPU usage --
>> having panicked VMs spinning in useless loops wastes their money. In shared
>> envs, those wasted cycles could be used by other processes/VMs. But this
>> is as much about the cloud as it is for laptops/embedded/anywhere -- Linux
>> should avoid wasting resources wherever possible.
> 
> So I don't really buy the laptop and embedded case, people tend to look
> at laptops when open, and get very impatient when they don't respond.
> Embedded things really should have a watchdog.
> 
> Also, should you not be using panic_timeout to auto reboot your machine
> in all these cases?
> 
> In any case, the VM nonsense, do they not have a virtual watchdog to
> 'reap' crashed VMs or something?

The key word here is "should." Should embedded systems have a watchdog?
Maybe. Should I've auto reboot set? Maybe. Perhaps I don’t want to reboot
until I’ve root-caused the crash. But my patch set isn’t about “shoulds.”
What I’m discussing here is (1) the default Linux behavior, and (2)
providing people with the flexibility to do what THEY think they should do,
not what you think they should do.

Thanks,
Carlos