linux-kernel - Re: [PATCH 0/4] x86/platform/UV: Update TSC support

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Message-ID: <20170929184104.GX6524@worktop.programming.kicks-ass.net>
Date:   Fri, 29 Sep 2017 20:41:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Travis <mike.travis@....com>
Cc:     Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andrew Banman <andrew.banman@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        kevin.b.stanton@...el.com
Subject: Re: [PATCH 0/4] x86/platform/UV: Update TSC support

On Fri, Sep 29, 2017 at 10:39:28AM -0700, Mike Travis wrote:
> >That's where it comes from. But normal systems really _should_ have it
> >at 0 and its a useful sanity check IMO. We really want to know when the
> >BIOS does a funny behind our backs.
> >
> 
> How about a more generic flag, such as "multi_tsc_sync_sources"?  That could
> trigger both disabling the "TSC == 0 on socket 0" check as well as disabling
> X86_FEATURE_ART where appropriate?  Or I could clear the feature ART cap
> separately in the UV system init code if they are not really related?

I _think_ the X86_FEATURE_ART is an artificial flag. We key off of
cpuid_level here.

So that multi_tsc_sync_sources or a more explicit is_uv_system() would
be required.