[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] cpufreq support status
>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 17.10.07 17:22 >>> >On 17/10/07 16:11, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote: > >>> It's definitely k8-powernow only right now. acpi-cpufreq might work if the >>> control register is an i/o port. It won't work if the control register is an >>> MSR, since the MSR would not be whitelisted in the WRMSR emulation in >>> emulate_privileged_op(). >> >> Does ACPI have means to specify MSRs as the access mechanism? I don't >> recall platform specific behavior like this, I thought this was restricted to >> the set of types named ACPI_ADR_SPACE_* in Linux' include/acpi/actypes.h >> (and which already goes beyond what is in ACPI 3.0b). > >Well, kind of but not really. ACPI_ADR_SPACE_FIXED_HARDWARE is used, and >this is a cop-out in the ACPI spec which means 'the OS needs extra info from >the CPU vendor'. So typically for power management it means that CPUID must >be mined to discover whether e.g., PowerNow or EnhancedSpeedStep MSRs should >be used. Looking into this some more, I find that ACPI_ADR_SPACE_FIXED_HARDWARE is mostly unsupported in Linux except for C-state handling, in which case is resolves to MWAIT. >This effectively means that the range of possible power-management MSRs is >very limited (since they cannot be specified dynamically in the ACPI tables) >and Xen itself should easily be able to probe for and dynamically white-list >available MSRs as appropriate. Probably all that needs to be added is >support for EnhancedSpeedStep MSRs, since we already have PowerNow support. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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