Comment 9 for bug 651370

I forgot to add above: on the E5410 c1.xlarge's that do boot successfully, the kernel output contains:

Oct 26 07:37:55 ip-10-243-51-207 kernel: [ 0.210255] intel_idle: MWAIT substates: 0x2220
Oct 26 07:37:55 ip-10-243-51-207 kernel: [ 0.210257] intel_idle: does not run on family 6 model 23

Which I believe means that intel_idle figured out that it needs to disable itself on these. The E5506's are model 26 rather than 23. The intel_idle code has a case statement that switches on this model number. Model 23 (0x17) is commented out for "FUTURE_USE" and thus falls through to the "does not run" condition with the output above. Model 26 (0x1A) has a case statement and will attempt to use intel_idle support.