Date: Wed, 27 Sep 2017 20:05:48 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Pasha Tatashin <pasha.tatashin@oracle.com>, linux@armlinux.org.uk,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
        john.stultz@linaro.org, sboyd@codeaurora.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de,
        hpa@zytor.com
Subject: Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early
 in boot
Message-ID: <20170927180548.GM17526@worktop.programming.kicks-ass.net>
References: <1504116205-355281-1-git-send-email-pasha.tatashin@oracle.com>
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 <20170927125857.yvwefpejzskiduwu@hirez.programming.kicks-ass.net>
 <20170927131003.dxbvu7frcqgtiwaz@hirez.programming.kicks-ass.net>
 <aed54345-b752-e93a-8be7-96df9b083f6c@oracle.com>
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On Wed, Sep 27, 2017 at 09:52:36PM +0800, Dou Liyang wrote:
> We do not want to do that. Because, we use "notsc" to support Dynamic
> Reconfiguration[1].
> 
> AFAIK, this feature enables hot-add system board which contains CPUs
> and memories. But the CPUs in different board may have different TSCs
> which are not consistent with the TSC from the existing CPUs. If we hot-add
> a board directly, the machine may happen the inconsistency of
> TSC.
> 
> We make our effort to specify the same TSC value as existing one through
> hardware and firmware, but it is hard. So we recommend to specify
> "notsc" option in command line for users who want to use Dynamic
> Reconfiguration.

Oh gawd, that's horrific. And in my book a good reason to kill that
option.