Thanks Nico, this info is very helpful. I now know where to start reading. Best regards, Davíð
On Sat, Jan 13, 2018 at 05:13:01PM +0100, Nico Huber wrote: > Hi Davíð, > > On 13.01.2018 15:34, Davíð Steinn Geirsson wrote: > > I am hoping to build coreboot with hyper-threading (SMT) disabled. I > > guess this can be done by skipping over the right processor IDs in > > the for loop in intel_cores_init in > > src/cpu/intel/model_206ax/model_206ax_init.c:470 ? > > no, you can't just ignore (logical) cores there. I suppose they would > still be visible to the OS but not functional. > > It seems the PCH is supposed to tell the CPU package after reset how > many (logical) cores should be enabled. There is a register to override > the settings: SOFT_RESET_DATA. Setting bit 0 in that register + a reset > should disable hyper-threading. > > Though, this register is already used in set_flex_ratio_to_tdp_nominal() > in `src/cpu/intel/model_206ax/bootblock.c`. > > You can check if hyper-threading is enabled by looking at MSR 0x35 > (CORE_THREAD_COUNT) or CPUID (eax 0x0b, ecx 0x00 / 0x01). Both should > be documented in Intel's SDM [1]. > > You should combine the decision to disable HT with the already present > code for the flex ratio. If any of the two settings need to change, > program SOFT_RESET_DATA accordingly and perform a reset. > > Hope that helps, > Nico > > -- > coreboot mailing list: [email protected] > https://mail.coreboot.org/mailman/listinfo/coreboot -- coreboot mailing list: [email protected] https://mail.coreboot.org/mailman/listinfo/coreboot
