linux-kernel - Re: [RFC PATCH 14/23] watchdog/hardlockup: Decouple the hardlockup detector from perf

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Date:   Wed, 13 Jun 2018 18:19:01 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Borislav Petkov <bp@...e.de>,
        Tony Luck <tony.luck@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>, x86@...nel.org,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Jacob Pan <jacob.jun.pan@...el.com>,
        Don Zickus <dzickus@...hat.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Frederic Weisbecker <frederic@...nel.org>,
        Babu Moger <babu.moger@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Colin Ian King <colin.king@...onical.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        iommu@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 14/23] watchdog/hardlockup: Decouple the hardlockup
 detector from perf

On Wed, Jun 13, 2018 at 10:43:24AM +0200, Peter Zijlstra wrote:
> On Tue, Jun 12, 2018 at 05:57:34PM -0700, Ricardo Neri wrote:
> > The current default implementation of the hardlockup detector assumes that
> > it is implemented using perf events.
> 
> The sparc and powerpc things are very much not using perf.

Isn't it true that the current hardlockup detector
(under kernel/watchdog_hld.c) is based on perf? As far as I understand,
this hardlockup detector is constructed using perf events for architectures
that don't provide an NMI watchdog. Perhaps I can be more specific and say
that this synthetized detector is based on perf.

On a side note, I saw that powerpc might use a perf-based hardlockup
detector if it has perf events [1].

Please let me know if my understanding is not correct.

Thanks and BR,
Ricardo

[1]. https://elixir.bootlin.com/linux/v4.17/source/arch/powerpc/Kconfig#L218