Re: CentOS 7.2 HVM, PVM and/or PVHVM

From: Paolo Bonzini <pbonzini@redhat.com>
To: James Okken <James.Okken@dialogic.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"kvm-owner@vger.kernel.org" <kvm-owner@vger.kernel.org>
Subject: Re: CentOS 7.2 HVM, PVM and/or PVHVM
Date: Mon, 3 Apr 2017 18:59:18 +0200	[thread overview]
Message-ID: <8dd6cf57-2444-ef07-492b-d02f3a08c080@redhat.com> (raw)
In-Reply-To: <MWHPR0101MB3072AB333D75221454AA789A8D080@MWHPR0101MB3072.prod.exchangelabs.com>

On 03/04/2017 17:36, James Okken wrote:
> Thanks Paolo,
> 
> So are you saying that if I am running a very latency sensitive,
> real-time, voice and video over IP application, then fundamentally
> KVM is not the best way to go? I would be better off going with XEN?

No, I haven't said anything like that... Where did you infer it from? :)

In fact I said:

> the kernel knows it's running on KVM and is using some services from
> the hypervisor to improve performance or functionality.
> [virtio] is just a set of PCI devices whose design was optimized for
> virtualization

KVM has effectively all the benefits of paravirtualization while using
standard PC hardware and firmware.  The same holds for Xen too, there is
hardly any performance penalty from hardware emulation in HVM domains
compared to PVH, and both Xen PVH and Xen HVM should be faster than Xen PV.

KVM is used often with DPDK and other latency sensitive applications.  I
suggest you look into using nohz_full in the host and the guest, as well
as the Linux realtime patch.

Thanks,

Paolo