Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
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>,
        Chris Metcalf <cmetcalf@mellanox.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Christoph Lameter <cl@linux.com>,
        "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>
In-Reply-To: <20180129155431.GW2269@hirez.programming.kicks-ass.net>
References: <1516320140-13189-1-git-send-email-frederic@kernel.org>
        <20180124104608.038fb212@redhat.com>
        <20180129011024.GA2942@lerouge>
        <20180129103316.4d2f9153@redhat.com>
        <20180129155431.GW2269@hirez.programming.kicks-ass.net>
Organization: Red Hat
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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'.
>