[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 Mon, 14 Jan 2013 18:08:45 +0100 Stefan Bader <stefan.bader@xxxxxxxxxxxxx> wrote: > On 14.01.2013 17:34, Borislav Petkov wrote: > > On Mon, Jan 14, 2013 at 04:58:54PM +0100, Stefan Bader wrote: > >> Starting with kernel v3.7 the following commit added a quirk > >> to obtain the real frequencies of certain AMD systems: > >> > >> commit f594065faf4f9067c2283a34619fc0714e79a98d > >> Author: Matthew Garrett <mjg@xxxxxxxxxx> > >> Date: Tue Sep 4 08:28:06 2012 +0000 > >> > >> ACPI: Add fixups for AMD P-state figures > >> > >> When running bare-metal, on my Opteron 6128 test box results > >> in the frequencies remaining effectively unchanged: > >> [ 5.475735] P0: MSR(hi,lo): 8000015c-50004004 > >> [ 5.479049] P0: fid=0x4, did=0x0, freq: 2000 -> 2000 > >> [ 5.484001] P1: MSR(hi,lo): 8000014c-50004a4e > >> [ 5.487314] P1: fid=0xe, did=0x1, freq: 1500 -> 1500 > >> [ 5.492272] P2: MSR(hi,lo): 80000141-50005048 > >> [ 5.495584] P2: fid=0x8, did=0x1, freq: 1200 -> 1200 > >> [ 5.500540] P3: MSR(hi,lo): 80000138-50005844 > >> [ 5.503853] P3: fid=0x4, did=0x1, freq: 1000 -> 1000 > >> [ 5.508812] P4: MSR(hi,lo): 80000131-50005c40 > >> [ 5.512125] P4: fid=0x0, did=0x1, freq: 800 -> 800 > >> > >> However running as dom0 under Xen 4.2, reading this MSR returns > >> null: > >> [ 11.613068] P0: MSR(hi,lo): 00000000-00000000 > >> [ 11.613074] P0: fid=0x0, did=0x0, freq: 2000 -> 1600 > >> [ 11.613078] P1: MSR(hi,lo): 00000000-00000000 > >> [ 11.613081] P1: fid=0x0, did=0x0, freq: 1500 -> 1600 > >> [ 11.613085] P2: MSR(hi,lo): 00000000-00000000 > >> [ 11.613088] P2: fid=0x0, did=0x0, freq: 1200 -> 1600 > >> [ 11.613091] P3: MSR(hi,lo): 00000000-00000000 > >> [ 11.613094] P3: fid=0x0, did=0x0, freq: 1000 -> 1600 > >> [ 11.613098] P4: MSR(hi,lo): 00000000-00000000 > >> [ 11.613101] P4: fid=0x0, did=0x0, freq: 800 -> 1600 > >> > >> And this results in Xen failing to change the governor: > >> "(XEN) Fail change to ondemand governor" > >> > >> I suppose this ultimately requires some support in the hypervisor > >> to pass through the real values. But since this is at least on my > >> combination of Xen 4.2 + kernel v3.7+ and AMD family 0x10 CPU a > >> regression compared to older kernels, I wonder whether the > >> following change might be something that should go into mainline: > >> > >> --- a/drivers/acpi/processor_perflib.c > >> +++ b/drivers/acpi/processor_perflib.c > >> @@ -340,6 +340,9 @@ static void amd_fixup_frequency(struct > >> acpi_processor_px *px 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 & 0x8000000)) > >> + return; > > > > 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. > > This actually only started to work when the xen-processor module got > introduced to provide acpi information to the hypervisor. If I > remember correctly powernow-k8 did fail. > For the way I did the fix: the AMD BIOS docs seemed to indicate that > even for bare metal bit 63 would say whether the values are valid. So > I thought this is a nice coincidence that under Xen with all 0 this > matches that special case... ;) >From a first glance I think this fix is a valid approach. There are BIOSes which disable P-states via this bit, so we have to observe this for bare-metal, too. Let me think a bit more about this, however, and see whether there is a better solution to do the right thing (tm) under Xen. Getting back to you then. Thanks, Andre. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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