[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] kernel 3.7+ cpufreq regression on AMD system running as dom0
On Tue, Jan 15, 2013 at 07:18:39PM +0100, Borislav Petkov wrote: > On Tue, Jan 15, 2013 at 12:53:05PM -0500, Konrad Rzeszutek Wilk wrote: > > > I don't think that's the right change - this is fixing baremetal so that > > > it works on xen. And besides, this code was in powernow-k8 before so I'm > > > wondering why did it work then. > > > > Powernow-k8 only populated the cpufreq policy information. This library > > (processor_perflib) is the generic library used for ACPI P-states parsing. > > This specific function (acpi_processor_get_performance_states) is just > > used to fetch and parse the P-states. > > > > Xen-acpi-processor (which we use to upload the P and C-states to the > > hypervisor) ends up calling this library to parse the P-states > > and this unfortunate quirk clamps the P-states based on the MSRS. > > Huh? This is a fix for _PSS frequency values which are rounded and thus > imprecise. The _PSS objects are the unfortunate ones, as most of the > other crap BIOS produces. I did not explain myself well. The fix is OK - it just that the hypervisor causes the quirk to not work correctly. Hmm, I wonder if there BIOSes that do the same thing (cause the MSR to return 0). Per you estimation of BIOS quality, it seems that this could happen. > > > It is odd that this CPU specific quirk got added in this generic > > library. Is there no ACPI quirk system similar to how DMI quirks are > > handled? > > Even if there were, do you know all the boards and BIOS revisions which > have those rounded values? The fix addresses the hardware which has > those 50MHz multiples and simply ignores the _PSS data but reads out the > P-states directly from the hardware. Oh, I was not thinking DMI per-say. I was thinking something similar to DMI-quirk API. But for the ACPI subsystem, so it would be: if (ARM) ... these quirks neccessary if (AMD) .. these quirks and then the ACPI code can make the calls to this ACPI-quirk API to figure out whether it needs to modulate values. But this is all hand-waving at this point. > > > Anyhow, I think this patch makes sense - it makes sure that the MSR > > value is sane. > > I agree to a certain degree. Testing the Valid bit is something we > should do for P-state MSRs - and for all MSRs containing a Valid bit, > for that matter - and the original code didn't do it. OK. > > However, you need to push down the *correct* frequencies *after* the > quirk to the hypervisor (I'm looking at push_pxx_to_hypervisor()) so > that it is aware of the exact P-state frequencies this CPU supports and > not some rounded values. Yes! It could be done in the hypervisor (it does the MSRs and figures out that the P-states need tweaking). > > AFAICT for the xen part, of course. But the baseline stands: you need to > tell the thing that switches P-states the exact P-state frequencies of > the CPU. :-). Right, that information is gathered from the MSRs. I think the Xen would need to do this since it can do the MSRs correctly and modify the P-states. So something like this in the hypervisor maybe (not even tested): diff --git a/xen/arch/x86/acpi/cpufreq/powernow.c b/xen/arch/x86/acpi/cpufreq/powernow.c index a9b7792..54e7808 100644 --- a/xen/arch/x86/acpi/cpufreq/powernow.c +++ b/xen/arch/x86/acpi/cpufreq/powernow.c @@ -146,7 +146,40 @@ static int powernow_cpufreq_target(struct cpufreq_policy *policy, return 0; } +#define MSR_AMD_PSTATE_DEF_BASE 0xc0010064 +static void amd_fixup_frequency(struct xen_processor_px *px, int i) +{ + u32 hi, lo, fid, did; + int index = px->control & 0x00000007; + + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) + return; + + if ((boot_cpu_data.x86 == 0x10 && boot_cpu_data.x86_model < 10) + || boot_cpu_data.x86 == 0x11) { + rdmsr(MSR_AMD_PSTATE_DEF_BASE + index, lo, hi); + /* Bit 63 indicates whether contents are valid */ + if (!(hi & 0x80000000)) + return; + + fid = lo & 0x3f; + did = (lo >> 6) & 7; + if (boot_cpu_data.x86 == 0x10) + px->core_frequency = (100 * (fid + 0x10)) >> did; + else + px->core_frequency = (100 * (fid + 8)) >> did; + } +} + +static void amd_fixup_freq(struct processor_performance *perf) +{ + int i; + + for (i = 0; i < perf->state_count; i++) + amd_fixup_frequency(perf->states, i); + +} static int powernow_cpufreq_verify(struct cpufreq_policy *policy) { struct acpi_cpufreq_data *data; @@ -158,6 +191,8 @@ static int powernow_cpufreq_verify(struct cpufreq_policy *policy) perf = &processor_pminfo[policy->cpu]->perf; + amd_fixup_freq(perf); + cpufreq_verify_within_limits(policy, 0, perf->states[perf->platform_limit].core_frequency * 1000); _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |