linux-kernel - Re: [GIT PULL] timer fixes

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Message-ID: <CAHk-=wgH8bSsgxnUAjuoUyDwHPKZwdVirH__=mJQu7RCFfCwZA@mail.gmail.com>
Date:   Tue, 17 Dec 2019 12:16:52 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [GIT PULL] timer fixes

On Tue, Dec 17, 2019 at 11:30 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> What alternatives are there? That is, we normally only use HPET to
> double check nobody messed up the TSC.

The thing is HPET seems to be _less_ reliable than the TSC we're
checking these days.

If that's the only use-case for HPET, we should just stop doing it.

> We can't just blindly trust TSC across everything x86.

No, but we can trust it when it's a modern CPU.

The HPET seems to get disabled on all the modern platforms, why do we
even have it enabled by default?

We should do the HPET cross-check only when we know the TSC might be
unreliable, I suspect.

           Linus