linux-kernel - Re: [PATCH] hardlockup: detect hard lockups using secondary (buddy) cpus

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Date:   Sun, 7 May 2023 10:12:29 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Ian Rogers <irogers@...gle.com>, ravi.v.shankar@...el.com,
        ricardo.neri@...el.com, Stephane Eranian <eranian@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-arm-kernel@...ts.infradead.org,
        kgdb-bugreport@...ts.sourceforge.net,
        Marc Zyngier <maz@...nel.org>,
        linux-perf-users@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        Will Deacon <will@...nel.org>, ito-yuichi@...itsu.com,
        Sumit Garg <sumit.garg@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Colin Cross <ccross@...roid.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Tzung-Bi Shih <tzungbi@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Ingo Molnar <mingo@...nel.org>,
        John Ogness <john.ogness@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Marco Elver <elver@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] hardlockup: detect hard lockups using secondary (buddy)
 cpus


On Mon, Apr 24, 2023 at 08:23:59AM -0700, Doug Anderson wrote:
> HPET system seems to have a single CPU in charge of processing the
> main NMI and then that single CPU is in charge of checking all the
> others. If that single CPU goes out to lunch then the system couldn't
> detect hard lockups.
> 
> In any case, I'm happy to let others debate about the HPET system. For
> now, I'll take my action items to be:

We don't really seem to make any progress on the HPET series, so even
if it is better in some way a series that is never merged is always
worse than one that is.

My experience is that cases where everything locks up are very rare.
I suspect as long as we cover the garden variety single CPU lockup case well
it is likely very diminishing returns to handle more complex cases. So whatever
gets the job done is fine.

Yes freeing the Perfmon resources is big advantage of either.

-Andi