hi all I just lost hours trying to understand why my kernel was seeing only 1 core in my ATOM 330 CPU The doc at http://www.gentoo.org/doc/en/kernel-config.xml#doc_chap3 i pretty goo and helped me but is missing a very important thing : "If any OS boots on the Atom without ACPI enabled (like say, the OpenWRT firmware), it will only see a single core." ( found on https://forum.openwrt.org/viewtopic.php?pid=92283 , thanks openwrt ;) http://www.columbia.edu/~ariel/acpi/acpi_howto.txt also helped with : "In very specific cases you may be required to enable ACPI for your system to function properly. 64-bit Itanium platforms require this; you won't get a choice in the kernel configuration menu to choose it or not, it will just be done for you. NUMA-enabled systems often require it, and systems with new Intel processors that support hyperthreading require it because they use ACPI tables for virtual processor discovery." I can says this is true for a hyperthreaded ATOM 330 ( 4 logical CPUs ) , but it seems to also be true for many others hyperthreaded CPUs ( all intel ? dont know ) so, section 3.6 says of gentoo doc says : "In all of these cases, you need to select the appropriate kernel options to obtain optimum performance from these setups. :
(continued) so, section 3.6 of of gentoo doc on http://www.gentoo.org/doc/en/kernel-config.xml#doc_chap3 says : "In all of these cases, you need to select the appropriate kernel options to obtain optimum performance from these setups. : Processor type and features ---> [*] Symmetric multi-processing support Select the above option if you are on a multi-processor system (of any type) [*] SMT (Hyperthreading) scheduler support Select the above option if you are on an Intel Hyper-Threading CPU [*] Multi-core scheduler support (NEW) Select the above option if your CPU is dual core please add this so I could be the last one loosing 15 hours finding this : " if you dont have ACPI enabled, your kernel will only see 1 core . . . even if you have 4 or more logical cpus and all the ht/smp options enabled in the kernel and in the bios . . . "
Thanks William, the change is now in. You'll see it on our web nodes in about an hour. Have fun and thanks for your report.
