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

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Message-ID: <alpine.DEB.2.21.1806191928040.10546@nanos.tec.linutronix.de>
Date:   Tue, 19 Jun 2018 19:32:49 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
cc:     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,
        peterz@...radead.org, 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 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, while with your change its
suddenly used in sched_clock().

I'm not opposed to that change but the changelog is completely misleading
as it suggest that this is a change which has no functional impact.

Thanks,

	tglx