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Date:   Tue, 19 Jun 2018 20:46:54 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Pavel Tatashin <pasha.tatashin@oracle.com>,
        steven.sistare@oracle.com, daniel.m.jordan@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, hpa@zytor.com, douly.fnst@cn.fujitsu.com,
        prarit@redhat.com, feng.tang@intel.com, pmladek@suse.com,
        gnomes@lxorguk.ukuu.org.uk
Subject: Re: [PATCH v10 1/7] x86/tsc: remove tsc_disabled flag
Message-ID: <20180619184654.GG2494@hirez.programming.kicks-ass.net>
References: <20180615174204.30581-1-pasha.tatashin@oracle.com>
 <20180615174204.30581-2-pasha.tatashin@oracle.com>
 <alpine.DEB.2.21.1806191928040.10546@nanos.tec.linutronix.de>
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On Tue, Jun 19, 2018 at 07:32:49PM +0200, Thomas Gleixner wrote:
> On Fri, 15 Jun 2018, Pavel Tatashin wrote:
> 
> > tsc_disabled is set when notsc is passed as kernel parameter. The reason we
> > have notsc is to avoid timing problems on multi-socket systems.  We already
> > have a mechanism, however, to detect and resolve these issues by invoking
> > tsc unstable path. Thus, make notsc to behave the same as tsc=unstable.
> 
> notsc also excludes TSC from being used at all

It does not; there is TSC usage even if you boot with notsc on. See how
it does not clear X86_FEATURE_TSC for instance.