linux-kernel - Re: [GIT PULL] isolation: 1Hz residual tick offloading v4

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Message-ID: <20180129155431.GW2269@hirez.programming.kicks-ass.net>
Date:   Mon, 29 Jan 2018 16:54:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luiz Capitulino <lcapitulino@...hat.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Lameter <cl@...ux.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [GIT PULL] isolation: 1Hz residual tick offloading v4

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.

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