linux-kernel - Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S machine

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Date:   Tue, 11 Oct 2022 22:11:43 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Zhang Rui <rui.zhang@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <tim.c.chen@...el.com>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Yu Liao <liaoyu15@...wei.com>
Subject: Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S
 machine

On Tue, Oct 11, 2022 at 04:01:46PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 11, 2022 at 09:33:26PM +0800, Zhang Rui wrote:
> 
> > topology_max_packages() or variable logical_packages can tell the
> > maximum packages.
> > But this check_system_tsc_reliable() is done in early boot phase where
> > we have boot cpu only. And the cpu topology is not built up at this
> > stage.
> 
> Is there a problem with disabling the TSC watchdog later in boot --
> after SMP bringup for example?
 
Currently the watchdog is disabled inside tsc_init(), right before
'tsc-early' clocksrouce is registered, otherwise it starts to be
monitored by 'jiffies' as watchdog. And there has been many cases
that 'jiffies' watchdog misjudged tsc as 'unstable' in early boot
phase, including recent Yu Liao's report on a 4 socket Skylake
server.

Thanks,
Feng