linux-kernel - Re: [PATCH v14 20/25] x86/tsc: calibrate tsc only once

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Message-ID: <20180723102841.58ea373b@alans-desktop>
Date:   Mon, 23 Jul 2018 10:28:41 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org,
        Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, hpa@...or.com, douly.fnst@...fujitsu.com,
        prarit@...hat.com, feng.tang@...el.com,
        Petr Mladek <pmladek@...e.com>, linux-s390@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com, pbonzini@...hat.com
Subject: Re: [PATCH v14 20/25] x86/tsc: calibrate tsc only once

> >> If we determined tsc early in boot using one of the quick methods:
> >> from cpuid/msr/quick_pit, can we assume that frequencies of all other
> >> CPUs will be determined the same way? Or do we still have to fallback

Not on 32bit at least. You can have a mixed slot 1 SMP system such as
an ASUS BP6 with cores at say 300 and 450MHz.

Now whether you'll find any such system in the world today is another
question.

Alan