incorrect cpu count ubuntu 11.04 new install

command and response

uname -a
Linux sidhartha 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:24 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r b swpd free buff cache si so bi bo in cs us sy id wa
 4 0 0 4180904 94104 2787924 0 0 128 629 692 3112 8 6 82 3

cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 42
model name : Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
stepping : 7
cpu MHz : 2693.762
cache size : 4096 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 1
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc up arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 x2apic popcnt aes xsave avx lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
bogomips : 5387.52
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

grep -c processor /proc/cpuinfo
1

cat /proc/cpuinfo | grep processor | wc -l
1

Are there any bugs reported?

I have not found any with this same issue I have found many with high cpu usage but this is not reporting the correct number of cores

Have you tried a Maverick LiveCD to test?

I have tried Maverick but can not get live CD to load as it fails on video card. I have loaded 10.04 and it shows correct number of cores. Not sure if this make any difference but I had to pass grub this argument to load the OS GRUB_CMDLINE_LINUX="acpi=off". I did not think that could have an effectt on cpu cores.

In debugging the acpi situation I found this link: https://wiki.ubuntu.com/DebuggingACPI and using the acpi=noirq the system now sees the 4 cores correctly. This is one of many issues around a new install on a dell xps 15z but it is forward movement.

Great share, this will help others to get fixed up if they come across this post.

Please mark as solved if it is so. I also suggest you log a bug and state your fix.