From: Luming Yu <luming.yu@gmail.com>
To: Feng Tang <feng.tang@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
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>,
"the arch/x86 maintainers" <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
paulmck@kernel.org, rui.zhang@intel.com, andi.kleen@intel.com,
Len Brown <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: Wed, 1 Dec 2021 23:47:39 -0500 [thread overview]
Message-ID: <CAJRGBZznZOxqfOE471jUUTupPeZ-zW31sRo+0p5o0SeFKSqF9w@mail.gmail.com> (raw)
In-Reply-To: <20211117023751.24190-2-feng.tang@intel.com>
On Tue, Nov 16, 2021 at 11:18 PM Feng Tang <feng.tang@intel.com> wrote:
>
> There are cases that tsc clocksources are wrongly judged as unstable by
> clocksource watchdogs like hpet, acpi_pm or 'refined-jiffies'. While
> there is hardly a general reliable way to check the validity of a
> watchdog, and to protect the innocent tsc, Thomas Gleixner proposed [1]:
>
> "I'm inclined to lift that requirement when the CPU has:
>
> 1) X86_FEATURE_CONSTANT_TSC
> 2) X86_FEATURE_NONSTOP_TSC
> 3) X86_FEATURE_NONSTOP_TSC_S3
> 4) X86_FEATURE_TSC_ADJUST
> 5) At max. 4 sockets
>
> After two decades of horrors we're finally at a point where TSC seems
> to be halfway reliable and less abused by BIOS tinkerers. TSC_ADJUST
> was really key as we can now detect even small modifications reliably
> and the important point is that we can cure them as well (not pretty
> but better than all other options)."
>
> As feature #3 X86_FEATURE_NONSTOP_TSC_S3 only exists on several generations
> of Atom processor, and is always coupled with X86_FEATURE_CONSTANT_TSC
> and X86_FEATURE_NONSTOP_TSC, skip checking it, and also be more defensive
> to use maxim of 2 sockets.
>
> The check is done inside tsc_init() before registering 'tsc-early' and
> 'tsc' clocksources, as there were cases that both of them had been
> wrongly judged as unreliable.
>
> For more background of tsc/watchdog, there is a good summary in [2]
>
> [1]. https://lore.kernel.org/lkml/87eekfk8bd.fsf@nanos.tec.linutronix.de/
> [2]. https://lore.kernel.org/lkml/87a6pimt1f.ffs@nanos.tec.linutronix.de/
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
> Change log:
>
> v3:
> * rebased against 5.16-rc1
> * refine commit log
>
> v2:
> * Directly skip watchdog check without messing flag
> 'tsc_clocksource_reliable' (Thomas)
>
> arch/x86/kernel/tsc.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
retry:
Reviewed-by: Luming Yu <luming.yu@intel.com>
next prev parent reply other threads:[~2021-12-02 4:44 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
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 ` Luming Yu [this message]
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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