linux-kernel - Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT

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Message-ID: <20170925083557.e6zwudms2pyxnhju@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Sep 2017 10:35:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, mingo@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO
 hypercall

On Sun, Sep 24, 2017 at 10:52:58PM -0300, Marcelo Tosatti wrote:
> On Fri, Sep 22, 2017 at 02:59:51PM +0200, Peter Zijlstra wrote:

> > Your patch is voodoo programming. You don't solve the actual problem,
> > you try and paper over it.
> 
> Priority boosting on a particular section of code is voodoo programming? 

Yes, because there's nothing that prevents said section of code from
triggering the exact problem you're trying to avoid.

The real fix is making sure the problem cannot happen to begin with,
which is done by fixing the interaction between the VCPU and that
emulation thread thing.