linux-kernel - Re: Current mainline git (24e700e291d52bd2) hangs when building e.g. perf

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Date:   Tue, 12 Sep 2017 09:14:38 +0200
From:   Markus Trippelsdorf <markus@...ppelsdorf.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: Current mainline git (24e700e291d52bd2) hangs when building e.g.
 perf

On 2017.09.09 at 11:26 -0700, Linus Torvalds wrote:
> On Sat, Sep 9, 2017 at 11:14 AM, Markus Trippelsdorf
> <markus@...ppelsdorf.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