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Date: Tue, 12 Sep 2017 09:14:38 +0200
From: Markus Trippelsdorf <markus@trippelsdorf.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: Current mainline git (24e700e291d52bd2) hangs when building e.g.
 perf
Message-ID: <20170912071438.GA282@x4>
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On 2017.09.09 at 11:26 -0700, Linus Torvalds wrote:
> On Sat, Sep 9, 2017 at 11:14 AM, Markus Trippelsdorf
> <markus@trippelsdorf.de> wrote:
> >
> > I think the issue gets fixed by:
> >
> >  # wrmsr -a 0xc0010015 0x1000018
> >
> > Setting bit 3 of the Hardware Configuration Register to 1.
> >
> > Quote from the docs:
> > ?TlbCacheDis: cacheable memory disable. Read-write. 0=Enables performance optimization that
> > assumes PML4, PDP, PDE, and PTE entries are in cacheable WB-DRAM
> 
> Uhhuh.
> 
> The page directories should *definitely* always be in cacheable
> memory, so it should be ok for that bit to be 0, and it's possible
> that setting it to 1 will seriously screw up performance.

Well, I don't see any dramatic performance decrease on my box.
For instance compile times are roughly the same (a bit quicker in fact).
And in day to day usage I notice absolutely no difference.

-- 
Markus