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Message-ID: <1587566950.9537.107.camel@suse.cz>
Subject: Re: [BISECTED]: Kernel panic (was: Linux 5.7-rc2)
From:   Giovanni Gherdovich <ggherdovich@suse.cz>
To:     Dave Kleikamp <dave.kleikamp@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Harald Arnesen <harald@skogtun.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date:   Wed, 22 Apr 2020 16:49:10 +0200
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On Wed, 2020-04-22 at 09:12 -0500, Dave Kleikamp wrote:
> On 4/22/20 4:02 AM, Giovanni Gherdovich wrote:
> > Linus, Peter:
> > 
> > the panic seen by Harald Arnesen (and Dave Kleikamp) is unrelated to
> > virtualization, and happens on all machines that have a CPU with less than 4
> > physical cores. It's a very serious (and very stupid) bug in the original
> > version of my code and is fixed by patch 2/4 "x86, sched: Account for CPUs
> > with less than 4 cores in freq. invariance" in the series 
> > 
> > https://lore.kernel.org/lkml/20200416054745.740-1-ggherdovich@suse.cz
> > 
> > Harald, Dave:
> > 
> > for peace of mind, can you please share the output of
> > 
> >   turbostat --interval 1 sleep 0
> 
> This is a Lenovo T410.
> 
> turbostat version 20.03.20 - Len Brown <lenb@kernel.org>
> CPUID(0): GenuineIntel 0xb CPUID levels; 0x80000008 xlevels; family:model:stepping 0x6:25:5 (6:37:5)
> [...]
> cpu0: MSR_TURBO_RATIO_LIMIT: 0x00001416
> 20 * 133.3 = 2666.6 MHz max turbo 2 active cores
> 22 * 133.3 = 2933.3 MHz max turbo 1 active cores


2 cores/ 4 threads, reported 4C turbo frequency of zero (i.e. bits 31:24
in MSR_TURBO_RATIO_LIMIT). This is consistent with all other occurrences
of this bug that have been reported.

Thanks Dave for your reply.


Giovanni