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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andi Kleen <ak@linux.intel.com>,
        "Paul E. McKenney" <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@fb.com, neeraju@codeaurora.org,
        feng.tang@intel.com, zhengjun.xing@intel.com,
        Chris Mason <clm@fb.com>
Subject: Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog
In-Reply-To: <20210426040736.GS1401198@tassilo.jf.intel.com>
References: <20210425224540.GA1312438@paulmck-ThinkPad-P17-Gen-1> <20210425224709.1312655-1-paulmck@kernel.org> <20210426040736.GS1401198@tassilo.jf.intel.com>
Date:   Mon, 26 Apr 2021 09:13:56 +0200
Message-ID: <874kftv7pn.ffs@nanos.tec.linutronix.de>
MIME-Version: 1.0
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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