From: Thomas Gleixner <tglx@linutronix.de>
To: Waiman Long <longman@redhat.com>, paulmck@kernel.org
Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org,
sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com,
maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org,
ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
x86@kernel.org
Subject: Re: [PATCH v2 clocksource 6/7] clocksource: Verify HPET and PMTMR when TSC unverified
Date: Thu, 02 Feb 2023 08:57:39 +0100 [thread overview]
Message-ID: <87h6w4zeh8.ffs@tglx> (raw)
In-Reply-To: <39752908-cc10-d63f-d02e-381693060af8@redhat.com>
On Wed, Feb 01 2023 at 22:40, Waiman Long wrote:
> On 2/1/23 14:55, Paul E. McKenney wrote:
>>>>> Therefore, when watchdog verification of TSC is disabled, enable it for
>>>>> HPET and PMTMR (AKA ACPI PM timer). This provides the needed in-kernel
>>>>> time-skew diagnostic without degrading the system's performance.
>>>> I'm more than unhappy about this. We finally have a point where the TSC
>>>> watchdog overhead can go away without adding TSC=reliable to the kernel
>>>> commandline.
>>>>
>>>> Now you add an unconditionally enforce the watchdog again in a way which
>>>> even cannot be disabled on the kernel command line.
>>>>
>>>> Patently bad idea, no cookies for you!
>>> I have a similar concern about this patch as well. That is why I was
>>> suggesting to have this enabled for a limited time after boot for sanity
>>> checking purpose only.
>> Fair enough!
>>
>> If the watchdog checking of HPET and/or PMTMR against TSC only happens
>> only when the sysadm asks for it, would you still want to have the ability
>> to enable such watchdog checking at boot time, and then to disable it
>> once the system had been running for some limited time?
>
> Yes, being optional is another way to avoid the overhead for the
> majority of users. The paranoids can turn it on if they want to.
Yes, opt-in is good enough.
Thanks,
tglx
next prev parent reply other threads:[~2023-02-02 8:07 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 0:27 [PATCH clocksource v2 0/7] Clocksource watchdog updates for v6.3 Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 1/7] clocksource: Print clocksource name when clocksource is tested unstable Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 2/7] clocksource: Loosen clocksource watchdog constraints Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 3/7] clocksource: Improve read-back-delay message Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 4/7] clocksource: Improve "skew is too large" messages Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 5/7] clocksource: Suspend the watchdog temporarily when high read latency detected Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 6/7] clocksource: Verify HPET and PMTMR when TSC unverified Paul E. McKenney
2023-01-26 10:57 ` Daniel Lezcano
2023-02-01 0:50 ` Paul E. McKenney
2023-02-01 10:24 ` Thomas Gleixner
2023-02-01 15:10 ` Feng Tang
2023-02-01 19:26 ` Waiman Long
2023-02-01 19:55 ` Paul E. McKenney
2023-02-02 3:40 ` Waiman Long
2023-02-02 4:54 ` Paul E. McKenney
2023-02-02 7:57 ` Thomas Gleixner [this message]
2023-02-04 1:27 ` Paul E. McKenney
2023-02-01 19:51 ` Paul E. McKenney
2023-01-25 0:27 ` [PATCH v2 clocksource 7/7] x86/tsc: Add option to force frequency recalibration with HW timer Paul E. McKenney
2023-02-03 4:36 ` PATCH v2 clocksource 8/7] clocksource: Enable TSC watchdog checking of HPET and PMTMR only when requested Paul E. McKenney
2023-02-06 19:57 ` Waiman Long
2023-02-07 1:08 ` Paul E. McKenney
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