linux-kernel - Re: [PATCH v2] KVM: x86: avoid redundant REQ

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Date:   Thu, 15 Dec 2016 15:32:45 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>, den@...tuozzo.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: avoid redundant REQ_EVENT



On 15/12/2016 15:30, Radim Krčmář wrote:
> 
> One useless round of KVM_REQ_EVENT is not going change nested
> performance by much and it is not the only thing we could improve wrt.
> TPR ... I would just leave it for now and take care of it when we
>  * don't to update PPR at all with APICv -- it is already correct
>  * drop the KVM_REQ_EVENT with flex priority, because lower TPR cannot
>    unmask an interrupt

I agree.  I still don't like the patch very much, because I feel like an
explicit state machine ("can KVM_REQ_EVENT do anything?") would be more
maintainable.  But if I don't come up with anything we'll go with this
patch.

Paolo