This is a multi-part message in MIME format. --------------090702030407000604010506 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/05/2012 03:55 PM, Laszlo Hornyak wrote:
----- Original Message -----
From: "Yaniv Kaul" <ykaul@redhat.com> To: "Laszlo Hornyak" <lhornyak@redhat.com> Cc: "Dan Kenigsberg" <danken@redhat.com>, "engine-devel" <engine-devel@ovirt.org> Sent: Wednesday, December 5, 2012 2:45:46 PM Subject: Re: [Engine-devel] host cpu feature
On 12/05/2012 03:39 PM, Laszlo Hornyak wrote:
----- Original Message -----
From: "Dan Kenigsberg" <danken@redhat.com> To: "Laszlo Hornyak" <lhornyak@redhat.com> Cc: "Yaniv Kaul" <ykaul@redhat.com>, "engine-devel" <engine-devel@ovirt.org> Sent: Wednesday, December 5, 2012 1:55:19 PM Subject: Re: [Engine-devel] host cpu feature
On Wed, Dec 05, 2012 at 06:46:09AM -0500, Laszlo Hornyak wrote:
----- Original Message -----
From: "Yaniv Kaul" <ykaul@redhat.com> To: "Laszlo Hornyak" <lhornyak@redhat.com> Cc: "engine-devel" <engine-devel@ovirt.org> Sent: Wednesday, December 5, 2012 12:23:47 PM Subject: Re: [Engine-devel] host cpu feature
On 12/05/2012 12:32 PM, Laszlo Hornyak wrote: > Hi, > > CPU-Host support allows the virtual machines to see and utilize > the > host's CPU flags, this enables better performance in VM's, at > the > price of worse portablity. > > http://www.ovirt.org/Features/Cpu-host_Support > > Your feedback is welcome! > > Thank you, > Laszlo > _______________________________________________ > Engine-devel mailing list > Engine-devel@ovirt.org > http://lists.ovirt.org/mailman/listinfo/engine-devel - I assume that when you allow migration, you'd use host-model? This is not clear from the design. It seems like we VDSM developers can choose to use either this or passthrough, while in practice we should support both. I join Kaul's question: it is an ovirt-level question whether hostPassthrough or hostModel or both should be supported. It should not be a unilateral vdsm decision. Ah, possibly misunderstanding, I did not mean that VDSM should decide whether to use host-passthrough or host-model. The engine should decide. I meant _you_ should decide which version of vdsm api modification do you want :)
If AllowMigrateCPUHost is set to true (in case you have the same cpu model everywhere in your DC) migration of such hsots will be enabled. Otherwise it will not be enabled. What is the breadth of AllowMigrateCPUHost? Engine wide? Per DC? Per cluster? I thought of eninge-wide. The of course you can have different models in two different DC, but they should be unique in one. We can add this to DC or cluster level, imho it would be just another checkbox on the UI that most users would not use.
I favor the latter; a user may have a cluster of exact-same hosts, where hostcpu migration is allowed, and other cluster where it is forbiden.
The nice thing about hostModel (unlike hostPassthrough) is that once we created the VM we can migrate it to stronger hosts, and back to the original host. I suppose that it complicates the scheduler. Yes with host-model you get the features that libvirt handles. In such cases the engine could decide, if you want this functionality. Well the scheduler architecture is just being reinvented.
For the host-passthrough, I think the AllowMigrateCPUHost configuration option would be a simple decision for the administrator: set it to true if all hosts are uniform. If it is not set to true, then we will not allow migration of such VMs. That's not what I understood from libvirt's documentation. I You may be right, could you send an URL to that point of the documentation or copy-paste?
The link I followed from your feature page: http://libvirt.org/formatdomain.html#elementsCPU : host-model The host-model mode is essentially a shortcut to copying host CPU definition from capabilities XML into domain XML. Since the CPU definition is copied just before starting a domain, exactly the same XML can be used on different hosts while still providing the best guest CPU each host supports. Neither match attribute nor any feature elements can be used in this mode. Specifying CPU model is not supported either, but model's fallback attribute may still be used. Libvirt does not model every aspect of each CPU so the guest CPU will not match the host CPU exactly. On the other hand, the ABI provided to the guest is reproducible. During migration, complete CPU model definition is transferred to the destination host so the migrated guest will see exactly the same CPU model even if the destination host contains more capable CPUs for the running instance of the guest; but shutting down and restarting the guest may present different hardware to the guest according to the capabilities of the new host. host-passthrough With this mode, the CPU visible to the guest should be exactly the same as the host CPU even in the aspects that libvirt does not understand. Though the downside of this mode is that the guest environment cannot be reproduced on different hardware. Thus, if you hit any bugs, you are on your own. Neither model nor feature elements are allowed in this mode. Y.
understood that if you want host+migration, you need to use host-model. Otherwise - host-passthrough. Y.
- I'm still convinced and commented on both relevat oVirt and libvirt BZs that we need to add x2apic support to the CPU, regardless of what the host CPU exposes. AFAIK, the KVM developers agree with me. Not quite sure how is this related... could you send some URL's for the bugreports?
--------------090702030407000604010506 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit <html> <head> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> </head> <body text="#000000" bgcolor="#FFFFFF"> <div class="moz-cite-prefix">On 12/05/2012 03:55 PM, Laszlo Hornyak wrote:<br> </div> <blockquote cite="mid:310221607.5986866.1354715753473.JavaMail.root@redhat.com" type="cite"> <pre wrap=""> ----- Original Message ----- </pre> <blockquote type="cite"> <pre wrap="">From: "Yaniv Kaul" <a class="moz-txt-link-rfc2396E" href="mailto:ykaul@redhat.com"><ykaul@redhat.com></a> To: "Laszlo Hornyak" <a class="moz-txt-link-rfc2396E" href="mailto:lhornyak@redhat.com"><lhornyak@redhat.com></a> Cc: "Dan Kenigsberg" <a class="moz-txt-link-rfc2396E" href="mailto:danken@redhat.com"><danken@redhat.com></a>, "engine-devel" <a class="moz-txt-link-rfc2396E" href="mailto:engine-devel@ovirt.org"><engine-devel@ovirt.org></a> Sent: Wednesday, December 5, 2012 2:45:46 PM Subject: Re: [Engine-devel] host cpu feature On 12/05/2012 03:39 PM, Laszlo Hornyak wrote: </pre> <blockquote type="cite"> <pre wrap=""> ----- Original Message ----- </pre> <blockquote type="cite"> <pre wrap="">From: "Dan Kenigsberg" <a class="moz-txt-link-rfc2396E" href="mailto:danken@redhat.com"><danken@redhat.com></a> To: "Laszlo Hornyak" <a class="moz-txt-link-rfc2396E" href="mailto:lhornyak@redhat.com"><lhornyak@redhat.com></a> Cc: "Yaniv Kaul" <a class="moz-txt-link-rfc2396E" href="mailto:ykaul@redhat.com"><ykaul@redhat.com></a>, "engine-devel" <a class="moz-txt-link-rfc2396E" href="mailto:engine-devel@ovirt.org"><engine-devel@ovirt.org></a> Sent: Wednesday, December 5, 2012 1:55:19 PM Subject: Re: [Engine-devel] host cpu feature On Wed, Dec 05, 2012 at 06:46:09AM -0500, Laszlo Hornyak wrote: </pre> <blockquote type="cite"> <pre wrap=""> ----- Original Message ----- </pre> <blockquote type="cite"> <pre wrap="">From: "Yaniv Kaul" <a class="moz-txt-link-rfc2396E" href="mailto:ykaul@redhat.com"><ykaul@redhat.com></a> To: "Laszlo Hornyak" <a class="moz-txt-link-rfc2396E" href="mailto:lhornyak@redhat.com"><lhornyak@redhat.com></a> Cc: "engine-devel" <a class="moz-txt-link-rfc2396E" href="mailto:engine-devel@ovirt.org"><engine-devel@ovirt.org></a> Sent: Wednesday, December 5, 2012 12:23:47 PM Subject: Re: [Engine-devel] host cpu feature On 12/05/2012 12:32 PM, Laszlo Hornyak wrote: </pre> <blockquote type="cite"> <pre wrap="">Hi, CPU-Host support allows the virtual machines to see and utilize the host's CPU flags, this enables better performance in VM's, at the price of worse portablity. <a class="moz-txt-link-freetext" href="http://www.ovirt.org/Features/Cpu-host_Support">http://www.ovirt.org/Features/Cpu-host_Support</a> Your feedback is welcome! Thank you, Laszlo _______________________________________________ Engine-devel mailing list <a class="moz-txt-link-abbreviated" href="mailto:Engine-devel@ovirt.org">Engine-devel@ovirt.org</a> <a class="moz-txt-link-freetext" href="http://lists.ovirt.org/mailman/listinfo/engine-devel">http://lists.ovirt.org/mailman/listinfo/engine-devel</a> </pre> </blockquote> <pre wrap="">- I assume that when you allow migration, you'd use host-model? This is not clear from the design. It seems like we VDSM developers can choose to use either this or passthrough, while in practice we should support both. </pre> </blockquote> </blockquote> <pre wrap="">I join Kaul's question: it is an ovirt-level question whether hostPassthrough or hostModel or both should be supported. It should not be a unilateral vdsm decision. </pre> </blockquote> <pre wrap="">Ah, possibly misunderstanding, I did not mean that VDSM should decide whether to use host-passthrough or host-model. The engine should decide. I meant _you_ should decide which version of vdsm api modification do you want :) </pre> <blockquote type="cite"> <blockquote type="cite"> <pre wrap="">If AllowMigrateCPUHost is set to true (in case you have the same cpu model everywhere in your DC) migration of such hsots will be enabled. Otherwise it will not be enabled. </pre> </blockquote> <pre wrap="">What is the breadth of AllowMigrateCPUHost? Engine wide? Per DC? Per cluster? </pre> </blockquote> <pre wrap="">I thought of eninge-wide. The of course you can have different models in two different DC, but they should be unique in one. We can add this to DC or cluster level, imho it would be just another checkbox on the UI that most users would not use. </pre> <blockquote type="cite"> <pre wrap="">I favor the latter; a user may have a cluster of exact-same hosts, where hostcpu migration is allowed, and other cluster where it is forbiden. The nice thing about hostModel (unlike hostPassthrough) is that once we created the VM we can migrate it to stronger hosts, and back to the original host. I suppose that it complicates the scheduler. </pre> </blockquote> <pre wrap="">Yes with host-model you get the features that libvirt handles. In such cases the engine could decide, if you want this functionality. Well the scheduler architecture is just being reinvented. For the host-passthrough, I think the AllowMigrateCPUHost configuration option would be a simple decision for the administrator: set it to true if all hosts are uniform. If it is not set to true, then we will not allow migration of such VMs. </pre> </blockquote> <pre wrap=""> That's not what I understood from libvirt's documentation. I </pre> </blockquote> <pre wrap=""> You may be right, could you send an URL to that point of the documentation or copy-paste?</pre> </blockquote> <br> The link I followed from your feature page: <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <a href="http://libvirt.org/formatdomain.html#elementsCPU">http://libvirt.org/formatdomain.html#elementsCPU</a> :<br> <br> host-model<br> The host-model mode is essentially a shortcut to copying host CPU definition from capabilities XML into domain XML. Since the CPU definition is copied just before starting a domain, exactly the same XML can be used on different hosts while still providing the best guest CPU each host supports. Neither match attribute nor any feature elements can be used in this mode. Specifying CPU model is not supported either, but model's fallback attribute may still be used. Libvirt does not model every aspect of each CPU so the guest CPU will not match the host CPU exactly. On the other hand, the ABI provided to the guest is reproducible. During migration, complete CPU model definition is transferred to the destination host so the migrated guest will see exactly the same CPU model even if the destination host contains more capable CPUs for the running instance of the guest; but shutting down and restarting the guest may present different hardware to the guest according to the capabilities of the new host.<br> host-passthrough<br> With this mode, the CPU visible to the guest should be exactly the same as the host CPU even in the aspects that libvirt does not understand. Though the downside of this mode is that the guest environment cannot be reproduced on different hardware. Thus, if you hit any bugs, you are on your own. Neither model nor feature elements are allowed in this mode.<br> <br> <br> Y.<br> <br> <blockquote cite="mid:310221607.5986866.1354715753473.JavaMail.root@redhat.com" type="cite"> <pre wrap=""> </pre> <blockquote type="cite"> <pre wrap="">understood that if you want host+migration, you need to use host-model. Otherwise - host-passthrough. Y. </pre> <blockquote type="cite"> <pre wrap=""> </pre> <blockquote type="cite"> <blockquote type="cite"> <blockquote type="cite"> <pre wrap="">- I'm still convinced and commented on both relevat oVirt and libvirt BZs that we need to add x2apic support to the CPU, regardless of what the host CPU exposes. AFAIK, the KVM developers agree with me. </pre> </blockquote> <pre wrap="">Not quite sure how is this related... could you send some URL's for the bugreports? </pre> </blockquote> </blockquote> </blockquote> <pre wrap=""> </pre> </blockquote> </blockquote> <br> </body> </html> --------------090702030407000604010506--