From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: questions about ack_intr_on_exit and preemption hooks Date: Fri, 13 Jul 2007 09:53:36 +0300 Message-ID: <46972170.6000108@qumranet.com> References: <20070712203417.GC28354@frankl.hpl.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: eranian-sDzT885Ts8HQT0dZR+AlfA@public.gmane.org Return-path: In-Reply-To: <20070712203417.GC28354-HU54gidqsKnWxDs0y9d3MAC/G2K4zDHf@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Stephane Eranian wrote: > Avi, > > A couple of months back, we had a discussion about PMU virtualization > and the difficulty I encountered trying to catch the PMU interrupt > vector in kvm on VM-exit. KVM does not set ack_intr_on_intr. Would > you mind reminding me of the reason for this? > > If we ack the interrupt, we have to dispatch it ourselves, most likely by faking an 'int $xx' instruction. By not acking the interrupt, we allow it do be delivered through the host IDT whether we are in guest mode or not. > On the topic of scheduler hooks for use by KVM, I think this > would help me also because it means I would not have to save > and restore the PMU registers on all VM-exit/VM-entry. At least > that is what I understood based on the discussion. Those registers > only need to be saved/restore when the KVM process is context switched. > If you want to monitor the guest, then I think you need to switch immediately on exit/entry, using the hardware msr switching mechanism. Otherwise, host events will be counted against the guest counters. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/