From: "Paul E. McKenney" <paulmck@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Feng Tang <feng.tang@intel.com>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
rui.zhang@intel.com, andi.kleen@intel.com, len.brown@intel.com,
tim.c.chen@intel.com
Subject: Re: [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms
Date: Tue, 30 Nov 2021 15:37:26 -0800 [thread overview]
Message-ID: <20211130233726.GD641268@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <87tuft9qpc.ffs@tglx>
On Wed, Dec 01, 2021 at 12:19:43AM +0100, Thomas Gleixner wrote:
> On Tue, Nov 30 2021 at 14:48, Paul E. McKenney wrote:
> > On Tue, Nov 30, 2021 at 10:55:45PM +0100, Thomas Gleixner wrote:
> >> > OK, HPET or nothing, then.
> >>
> >> Older machines also have pm_timer. But those beasts seem to have lost
> >> that too.
> >
> > I suppose that one way of avoiding clock-skew messages is to have only
> > one clock.
>
> Indeed. It's a complete mystery why it takes ages to implement reliable
> clocks in hardware.
That one is easy. It is because the previous clocksource watchdog was
too lenient. ;-)
(Sorry, couldn't resist...)
> >> >> We really need to remove the watchdog requirement for modern hardware.
> >> >> Let me stare at those patches and get them merged.
> >> >
> >> > You are more trusting of modern hardware than I am, but for all I know,
> >> > maybe rightfully so. ;-)
> >>
> >> Well, I rather put a bet on the hardware, which has become reasonable
> >> over the last decade, than on trying to solve a circular dependency
> >> problem with tons of heuristics which won't ever work correctly.
> >
> > Use of HPET to check the interval length would not be circular, right?
>
> As long as the HPET works reliably :)
Is it also a complete mystery why clocksources previously deemed
reliable no longer work reliably? ;-)
> >> TSC_ADJUST is a reasonable safety net and since its invention the amount
> >> of BIOS wreckage has been massively reduced. Seems the nastigram in
> >> dmesg when detecting a change in TSC_ADJUST had an effect or maybe
> >> Microsoft enforces a tinkerfree TSC by now and we get the benefit. :)
> >>
> >> I still wish to have a knob to lock down TSC to read only, but that's
> >> probably for christmas 2030 or later. :)
> >
> > Indeed. How would BIOS writers hide their SMI handlers? :-/
>
> TSC_ADJUST already ruined that party.
Give the BIOS writers time, they will figure something else out. :-(
Thanx, Paul
next prev parent reply other threads:[~2021-11-30 23:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 2:37 [PATCH v3 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked Feng Tang
2021-11-17 2:37 ` [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms Feng Tang
2021-11-30 6:46 ` Feng Tang
2021-11-30 14:40 ` Paul E. McKenney
2021-11-30 15:02 ` Feng Tang
2021-11-30 16:28 ` Paul E. McKenney
2021-11-30 20:39 ` Thomas Gleixner
2021-11-30 20:47 ` Paul E. McKenney
2021-11-30 21:55 ` Thomas Gleixner
2021-11-30 22:48 ` Paul E. McKenney
2021-11-30 23:19 ` Thomas Gleixner
2021-11-30 23:37 ` Paul E. McKenney [this message]
2021-12-01 1:26 ` Feng Tang
2021-12-01 17:52 ` Paul E. McKenney
2021-12-07 1:41 ` Feng Tang
2021-12-01 4:45 ` Luming Yu
2021-12-01 5:19 ` Feng Tang
2021-12-01 10:41 ` Thomas Gleixner
2021-12-01 23:47 ` [tip: x86/urgent] x86/tsc: Disable clocksource watchdog for TSC on qualified platorms tip-bot2 for Feng Tang
2021-12-02 4:47 ` [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms Luming Yu
2021-12-01 23:47 ` [tip: x86/urgent] x86/tsc: Add a timer to make sure TSC_adjust is always checked tip-bot2 for Feng Tang
2022-03-14 17:52 ` [PATCH v3 1/2] x86/tsc: add a timer to make sure tsc_adjust " Nicolas Saenz Julienne
2022-03-15 1:33 ` Feng Tang
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