linux-kernel - Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog

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Date:   Mon, 26 Apr 2021 09:13:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <ak@...ux.intel.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...com, neeraju@...eaurora.org,
        feng.tang@...el.com, zhengjun.xing@...el.com,
        Chris Mason <clm@...com>
Subject: Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog

On Sun, Apr 25 2021 at 21:07, Andi Kleen wrote:
>> occur between the reads of the two clocks.  Yes, interrupts are disabled
>> across those two reads, but there are no shortage of things that can
>> delay interrupts-disabled regions of code ranging from SMI handlers to
>> vCPU preemption.  It would be good to have some indication as to why
>
> I assume vCPU preemption here refers to preempt RT? I didn't think
> a standard kernel could preempt when interrupt are disabled.

Neither does Preempt-RT. It's about vCPU's being preempted by the
hypervisor which can happen anytime independent of the state of the
guest.

Thanks,

        tglx