Messages in this thread | | | Subject | Re: [PATCH] cpufreq: intel_pstate: Force intel_pstate to load when HWP disabled in firmware | From | Giovanni Gherdovich <> | Date | Thu, 13 May 2021 12:10:04 +0200 |
| |
On Thu, 2021-05-13 at 02:24 -0700, Srinivas Pandruvada wrote: > On Thu, 2021-05-13 at 09:59 +0200, Giovanni Gherdovich wrote: > > On CPUs succeeding SKX, eg. ICELAKE_X, intel_pstate doesn't load > > unless > > CPUID advertises support for the HWP feature. Some OEMs, however, may > > offer > > users the possibility to disable HWP from the BIOS config utility by > > altering the output of CPUID. > > Is someone providing a utility? What is the case for broken HWP?
Yes, I know of at least one server manufacturer that ships a BIOS config utility where the user can disable HWP.
On such server machine, which has an ICELAKE_X CPU, if the user unchecks HWP via BIOS then intel_pstate will refuse to load saying:
intel_pstate: CPU model not supported
because ICELAKE_X is not in the list intel_pstate_cpu_ids (defined in intel_pstate.c) of CPUs that intel_pstate supports when HWP is absent from CPUID; that list ends at SKYLAKE_X.
An alternative approach to register intel_pstate in the case I'm describing would be to add ICELAKE_X (and every CPU model after that, forever?) to the list intel_pstate_cpu_ids.
> It is possible that some user don't want to use HWP, because there > workloads works better without HWP. But that doesn't mean HWP is > broken.
That's true, a user may legitimate want to disable HWP, and we have the intel_pstate=no_hwp option for that. But for that option to work CPUID must still show that the CPU is HWP-capable; when disablement happens in BIOS, it's not the case.
The wording "hwp_broken_firmware" deliberately has a negative connotation (the intended meaning is: "firmware is broken, regarding HWP"), carrying the not-so-subtle message "OEM folks, please don't do this". My understanding is that the preferred way to disable HWP is with intel_pstate=no_hwp, the firmware should stay out of it.
I hope this clarifies the problem (there is an ICELAKE_X somewhere out there that can't load intel_pstate, which is not nice) and the intention (discouraging disablement of HWP via firmware).
Giovanni
| |