Question regarding sibling field in cpuinfo and hyperthreading enabled/disabledin bios

From: Richard Wohlstadter
Date: Mon Nov 21 2005 - 11:23:34 EST


I've recently been told that the siblings field in /proc/cpuinfo should have a count of 2 when hyperthreading is enabled in the bios of a machine and should drop to 1 when hyperthreading is disabled in the bios of a machine. I have a vendor who is using this algorithm to decide whether they should divide by 2 on the number of processors showing in /proc/cpuinfo to obtain the real count of physical processors in the machine. I've noticed on my Dell 2-cpu Xeon, that siblings field does not change when you enable/disable the hyperthreading feature in the bios (only the number of processors seen in /proc/cpuinfo). My question I guess is this a bug in the bios of my Dell box(should siblings count drop to 1 when hyperthreading is disabled?). I would think a better approach for the vendor would be to look at the physical ID field in /proc/cpuinfo since I've noticed that each real physical cpu has a different ID.

Please CC me on answers since I'm not on the list. Thanks for any insight you provide.

Rich Wohlstadter
Genome Sequencing Center
Washington University of Saint Louis
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