linux-kernel - Re: [RFC PATCH 0/2] KVM: Support Heterogeneous RT VCPU Configurations.

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Message-ID: <YQE1aB0/6B1FReZg@hirez.programming.kicks-ass.net>
Date:   Wed, 28 Jul 2021 12:46:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Suleiman Souhlal <suleiman@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        ssouhlal@...ebsd.org, joelaf@...gle.com, senozhatsky@...omium.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>
Subject: Re: [RFC PATCH 0/2] KVM: Support Heterogeneous RT VCPU
 Configurations.

On Wed, Jul 28, 2021 at 07:32:53AM -0300, Marcelo Tosatti wrote:
> Peter, not sure what exactly are you thinking of? (to solve this
> particular problem with pv deadline scheduling).
> 
> Shouldnt it be possible to, through paravirt locks, boost the priority
> of the non-RT vCPU (when locking fails in the -RT vCPU) ?

No. Static priority scheduling does not compose. Any scheme that relies
on the guest behaving 'nice' is unacceptable.