Date: Sat, 20 Mar 2010 16:22:20 +0000 From: Bruce Simpson <bms@incunabulum.net> To: freebsd-xen@freebsd.org Subject: Re: FreeBSD on Xen with hw virtualization support Message-ID: <4BA4F63C.1070407@incunabulum.net> In-Reply-To: <4BA4F5A6.508@incunabulum.net> References: <20100318204746.GA57903@cons.org> <e8f0b581003190547u42de13c5u2613d76913af1db5@mail.gmail.com> <ade45ae91003192110r774050dbld840aebcdfe7cb17@mail.gmail.com> <4BA4F5A6.508@incunabulum.net>
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On 03/20/10 16:19, Bruce Simpson wrote: > > There is a performance penalty, because Xen has to emulate real > hardware for HVM, using code largely cribbed from QEMU. > > Normally this happens within the hypervisor itself, however, this is > problematic, because there is then no good way to book the > CPU/memory/IO involved to the domU doing the I/O. This in turn affects > scheduling parameters. Correction: mostly dom0 with some hypervisor bits on top. But this still screws up HVM domU accounting. In a hosting environment, this is all important. Chisnall's Xen book explains this in great detail.
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