Description of problem: As says in subject, the kernel detects only one of 2 cores in a dual core CPU, as shown by "cat /proc/cpuinfo" -> processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 14 model name : Genuine Intel(R) CPU T2400 @ 1.83GHz stepping : 8 cpu MHz : 1830.975 cache size : 2048 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc up pni monitor vmx est tm2 xtpr bogomips : 3663.67 clflush size : 64 Version-Release number of selected component (if applicable): kernel-2.6.22.1-33.fc7 How reproducible: Always
Similar problems have been reported on Fedora 7 by others -> http://forums.fedoraforum.org/showthread.php?p=822704
This problem (detecting only 1 out of 2 cores) appeared when I booted the kernel with "acpi=off" option (originally needed for kernel-2.6.21-1.3194.fc7 due to bug 241249). I have verified now that this option is not needed for the kernel-2.6.22.1-33.fc7 to boot successfully. It seems that use of "acpi=off" is preventing the detection of both cores. If this option is not used then both cores are detected fine.
Detection of multiple processors requires ACPI on modern machines. Booting with kernel option "acpi=ht" might work by enabling only enough ACPI to detect the CPUs.