linux-kernel - Re: [PATCH v10 1/7] x86/tsc: remove tsc

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Date:   Tue, 19 Jun 2018 21:12:45 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, john.stultz@...aro.org,
        sboyd@...eaurora.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, hpa@...or.com, douly.fnst@...fujitsu.com,
        prarit@...hat.com, feng.tang@...el.com, pmladek@...e.com,
        gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v10 1/7] x86/tsc: remove tsc_disabled flag

On Tue, 19 Jun 2018, Peter Zijlstra wrote:
> 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.

Well, kinda. There is some stuff in the apic calibration which uses TSC
independent of tsc_disabled, but that's about it.

Thanks,

	tglx