I have a Z820 with a single 4 core hyperthreaded Processor on which I have installed openSUSE/Xen 4.2 In native boot up dmesg lists:- 0.044679] smpboot: CPU0: Intel(R) Xeon(R) CPU E5-2643 0 @ 3.30GHz (fam: 06, model: 2d, stepping: 07) [...] 0.154060] smpboot: Booting Node 0, Processors #1 #2 #3 #4 #5 #6 #7 OK [ 0.257167] Brought up 8 CPUs [ 0.257171] smpboot: Total of 8 processors activated (52670.73 BogoMIPS) ...but in Xen I get:- (XEN) Processor #0 6:13 APIC version 21 (XEN) Processor #2 6:13 APIC version 21 (XEN) Processor #4 6:13 APIC version 21 (XEN) Processor #6 6:13 APIC version 21 Implying that the hyperthreading "cpu''s" are being "ignored" A slightly older Z800 does not exhibit this behaviour, so I am wondering if this is a "feature" of the efi boot process, or if Xen is ignoring the hyperthreading as it may conflict its own thread scheduler. Looking through the archives suggests that efi may cause issues and I am wondering if this is one of them. Does anyone else have any experience of this? -- Tim