This is a BIOS bug. If you look more closely to the content of /proc/cpuinfo 
for the affected cores, you'll see that there are fewer reported CPU features, 
including the 'est' feature which is Enhanced SpeedStep. If you post what cpuid 
-r command dumps, you will probably see  that  the affected CPU cores report 
incorrect CPU features (CPUID leaf 1, that's EAX=1, features reported in ECX). 
This is caused by the AV69 / AX64 revision E0 CPU errata (L5430 is revE0, see 
the CPU signature 0x1067a) and the failure of the BIOS to update the microcode 
for all CPU cores (look at the dmesg log, microcode 0x0), before each revE0 
core gets to initialize the PECI_CTL MSR. It may be that your BIOS doesn't 
contain the required microcode update. The same thing can be said about the 
revC0 microcode update (CPU signature 0x10676), but the revC0 is not affected 
by the errata.
I have already investigated a case with an Abit IP35 motherboard, a revE0 Xeon 
CPU and a BIOS that contains the required microcode update, but which fails to 
update the microcode to cores 2,3 and 4, while the first core is a success. The 
only workaround I found was to modify the raw BIOS, not to write to the 
PECI_CTL MSR, and to disable all thermal control/protection, in the BIOS menu.

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https://bugs.launchpad.net/bugs/1367002

Title:
  Intel XEON L5430 is not supported

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