From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH v5 07/16] apic: Open-code timer save/restore Date: Mon, 19 Dec 2011 18:53:16 -0600 Message-ID: <4EEFDC7C.3020606@codemonkey.ws> References: <61e59db37279bb3834b996c84e9a0523638f5e35.1323952403.git.jan.kiszka@siemens.com> <4EEFB8FB.3030105@codemonkey.ws> <4EEFCC92.9030300@web.de> <4EEFD767.2050703@codemonkey.ws> <4EEFD7FA.9010407@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , Marcelo Tosatti , qemu-devel , Blue Swirl , Avi Kivity To: Jan Kiszka Return-path: In-Reply-To: <4EEFD7FA.9010407@web.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org On 12/19/2011 06:34 PM, Jan Kiszka wrote: > On 2011-12-20 01:31, Anthony Liguori wrote: >> On 12/19/2011 05:45 PM, Jan Kiszka wrote: >>> On 2011-12-19 23:21, Anthony Liguori wrote: >>>> On 12/15/2011 06:33 AM, Jan Kiszka wrote: >>>>> To enable migration between accelerated and non-accelerated APIC >>>>> models, >>>>> we will need to handle the timer saving and restoring specially and can >>>>> no longer rely on the automatics of VMSTATE_TIMER. Specifically, >>>>> accelerated model will not start any QEMUTimer. >>>>> >>>>> This patch therefore factors out the generic bits into apic_next_timer >>>>> and introduces a post-load callback that can be implemented differently >>>>> by both models. >>>>> >>>>> Signed-off-by: Jan Kiszka >>>> >>>> So you basically want the timer to be a dummy field for the in-kernel >>>> apic? >>>> >>>> Can you fix this up in a pre-save routine (put QEMUTimer into a state >>>> where there isn't an event pending)? >>> >>> It is not a dummy field, it contains the proper state in both cases. We >>> just need to convert it to an open-coded state to avoid the QEMUTimer >>> restoration magic in the in-kernel case (where there must be no >>> QEMUTimer). >> >> So the state gets fed into the kernel instead of userspace? > > Nope. It's kept for eventual use by a user space model. I think you misunderstood my comments. When you are using the in-kernel APIC, the is no implementation for the post_load hook. As far as I can tell, the state isn't used. I know it's used by the user space model but from what I can tell, the value is essentially sync with the in-kernel APIC almost immediately as it happens during KVM_RUN. So it's a QEMUTimer in the userspace model, but it's just an integer when used in the in-kernel APIC as the timer never fires. It is just saved/restored from and to the kernel. Is this correct? Regards, Anthony Liguori