linux-kernel - Re: [PATCH v3 1/2] x86/tsc: add a timer to make sure tsc

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Message-Id: <20220314175207.274870-1-nsaenzju@redhat.com>
Date:   Mon, 14 Mar 2022 18:52:07 +0100
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     feng.tang@...el.com, tglx@...utronix.de
Cc:     andi.kleen@...el.com, bp@...en8.de, dave.hansen@...el.com,
        hpa@...or.com, len.brown@...el.com, linux-kernel@...r.kernel.org,
        mingo@...hat.com, paulmck@...nel.org, peterz@...radead.org,
        rui.zhang@...el.com, tim.c.chen@...el.com, x86@...nel.org,
        mtosatti@...hat.com, nsaenzju@...hat.com, frederic@...nel.org
Subject: Re: [PATCH v3 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked

Hi Feng, Thomas,

> On Wed, Nov 17, 2021 at 10:37:51AM +0800, Feng Tang wrote:
> Normally the tsc_sync will get checked every time system enters idle state,
> but Thomas Gleixner mentioned there is still a caveat that a system won't
> enter idle [1], either because it's too busy or configured purposely to not
> enter idle. Setup a periodic timer (every 10 minitues) to make sure the
> check is always on.
> 
> [1]. https://lore.kernel.org/lkml/875z286xtk.fsf@nanos.tec.linutronix.de/
> Signed-off-by: Feng Tang <feng.tang@...el.com>

I can see this timer interrupting my system's nohz_full CPUs. It'd be nice to
be able to avoid the noise. A solution is using 'tsc=reliable', but IIUC this
is not what the flag was created for. Any ideas/suggestions?

Regards,
Nicolas