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Date: Mon, 29 Jan 2018 11:27:34 -0500
From: Luiz Capitulino <lcapitulino@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
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        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Wanpeng Li <kernellwp@gmail.com>, Mike Galbraith <efault@gmx.de>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [GIT PULL] isolation: 1Hz residual tick offloading v4
Message-ID: <20180129112734.27553e0e@redhat.com>
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On Mon, 29 Jan 2018 16:54:31 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Jan 29, 2018 at 10:33:16AM -0500, Luiz Capitulino wrote:
> > Cool, passing tsc=reliable worked for me. I finally got to the tick to
> > go completely away. While I agree that fixing that is beyond the scope
> > of this series, I think we should improve it anyway since it will probably
> > come up for people trying the new nohz_full=.  
> 
> The only way to fix that is to audit all BIOS code :/ Short of that, we
> need to periodically test the TSC on each CPU/SOCKET to verify its still
> in step with expectation.

Oh, OK. I thought we could find a way to avoid the timer in the kernel
for certain CPUs like mine.

Thanks for the explanation.

> 
> Sadly MSR_IA32_TSC and MSR_IA32_TSC_ADJUST are writable registers and
> BIOS monkeys occasionally write to them for 'raisins-of-insanity'.
>