linux-kernel - Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

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Message-Id: <540BB5C2-CEAE-47D2-845B-2DDEF3CDC303@gmail.com>
Date:   Tue, 21 Mar 2017 17:02:25 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     Gabriel Somlo <gsomlo@...il.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Joerg Roedel <joro@...tes.org>, KVM list <kvm@...r.kernel.org>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

> On Mar 21, 2017, at 3:51 PM, Gabriel Somlo <gsomlo@...il.com> wrote:
> 
> And I get the exact same results on the MacBookAir4,2 (which exhibits
> no freezing or extreme sluggishness when running OS X 10.7 smp with
> Michael's KVM MWAIT-in-L1 patch)...

Sorry for my confusion. I didn’t read the entire thread and thought that
the problem is spurious wake-ups.

Since that is not the case, I would just suggest two things that you can
freely ignore:

1. According to the SDM, when an interrupt is delivered, the interrupt
is only delivered on the following instruction, so you may consider
skipping the MWAIT first.

2. Perhaps the CPU changes for some reason GUEST_ACTIVITY_STATE (which
is not according to the SDM).

That is it. No more BS from me.

Nadav