linux-kernel - RE: [PATCH v1] KVM/x86/vPMU: Guest PMI Optimization

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Date:   Sat, 13 Oct 2018 02:21:19 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Xu, Like" <like.xu@...el.com>
Subject: RE: [PATCH v1] KVM/x86/vPMU: Guest PMI Optimization

On Saturday, October 13, 2018 12:31 AM, Andi Kleen wrote:
> > 4. Results
> >     - Without this optimization, the guest pmi handling time is
> >       ~4500000 ns, and the max sampling rate is reduced to 250.
> >     - With this optimization, the guest pmi handling time is ~9000 ns
> >       (i.e. 1 / 500 of the non-optimization case), and the max sampling
> >       rate remains at the original 100000.
> 
> Impressive performance improvement!
> 
> It's not clear to me why you're special casing PMIs here. The optimization
> should work generically, right?


Yes, seems doable. I plan to try some lazy approach for the perf event allocation. 

> Is that guaranteed to be always called on the right CPU that will run the vcpu?
> 
> AFAIK there's an ioctl to set MSRs in the guest from qemu, I'm pretty sure it
> won't handle that.
 

Thanks, will consider that case.

Best,
Wei