Re: [libvirt] [BUG] Xen x86_64 needs PAE?

Hello, Am Dienstag 24 August 2010 14:12:24 schrieb Daniel P. Berrange: I attached 8 files: 1. xen-fv-w2k8.broken.xml is my initial file, which was used with 'virsh define' + 'virsh start'. 2. xen-fv-w2k8.broken.xm was created using "virsh domxml-to-native xen-xm" 3. xen-fv-w2k8.broken.dump was created using "xm list --long Windows2008r2_64" 4. xen-fv-w2k8.fixed.xml with just '<pae/>' added, 'virsh define' + 'virsh start'. 5.-6. xen-fv-w2k8.fixed.{xm,dump} analog to above. 7. xen-fv-w2k8.clean.xm is without the pae=[01] line, so 'xm create' uses it's default. 8. xen-fv-w2k8.clean.dump of 'xm list --long' after 'xm create' 501 root@xen1=xen64:~ 0# xm info host : xen1 release : 2.6.32-ucs11-xen-amd64 version : #1 SMP Sat Jul 31 07:49:13 UTC 2010 machine : x86_64 hw_caps : 078bf3ff:ebd3fbff:00000000:00000010:00002001:0000001d:0000001d:00000000 virt_caps : hvm xen_major : 3 xen_minor : 4 xen_extra : .3 xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64 That is what I expected as well: neither for Windows 2k8 nor for Linux would I get a 64 bit guest. Only after adding the <pae/> feature it worked. Perhaps related: Setting "arch=x86_64" for Xen domains never made a difference for me: On the next "virsh dumpxml" that attribute was gone again making it impossible to distinguish between 32 and 64 bit Xen domains. If I understand pae right, x86_64 used a page-table-layout very similar to x86_32+pae, which makes doing the Virtual Memory mapping between host and guests easy. For x86_32 without pae you'd need to do some heavy reshuffling, because the page tables would be totally different. I noticed the pae problem during my testing: guests started via "xm create/start" ran fast, while guestss started via "virsh start" were very slow. As soon as one non-pae-guest was running, the whole system got unresponsive. It seemed to be related to the memory size, since running a guest with 128M or 512M made a huge difference. The missing <pae/> is translated to pae=0, which overwrites Xens default. Because of that my code currently tests for xen on x86_64 and than always adds <pae/> to make it work. My expectation would be that the capabilities XML should thus report <pae/>, if an application is supposed to add the <pae/> feature to get an 64 bit xen-fv domain. Sincerely Philipp -- Philipp Hahn Open Source Software Engineer hahn(a)univention.de Univention GmbH Linux for Your Business fon: +49 421 22 232- 0 Mary-Somerville-Str.1 28359 Bremen fax: +49 421 22 232-99 http://www.univention.de **** Besuchen Sie unsere Praxis-Vorträge zu UCS@School auf der FIT-ÖV am 23.09.2010 im Haus der Wissenschaft in Bremen ****