Messages in this thread |  | | Date | Fri, 10 Feb 2012 12:18:38 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH 5/8] ACPI: add processor driver for Xen virtual CPUs. |
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> + if (pr->id == -1) { > + int device_declaration; > + int apic_id = -1; > + > + if (!strcmp(acpi_device_hid(device), ACPI_PROCESSOR_OBJECT_HID)) > + device_declaration = 0; > + else > + device_declaration = 1; > + > + apic_id = acpi_get_cpuid(pr->handle, > + device_declaration, pr->acpi_id); > + if (apic_id == -1) { > + /* Processor is not present in MADT table */
So I was struggling to find an easy way to make the cases below (where VCPU != physical CPU) work with using the driver that iterates over the 'processor' and was mystified to why it would not work, even with this patchset. Found out that the acpi_get_cpuid does this:
201 #ifdef CONFIG_SMP 202 for_each_possible_cpu(i) { 203 if (cpu_physical_id(i) == apic_id) 204 return i; 205 }
and since not-online vCPUs (so dom0_max_vcpus) are not in the "possible" bitmask, we never get to check line 203 and end up returning -1 for offline/not-present/not-possible vCPUs.
Which means that we end up here: > + return 0; > + } > +
instead of going through the pr->id = 0.
By the end of this, the information that the hypervisor gets is actually limited to the amount of CPUs that we specified in dom0_max_vcpus=
> + /* > + * It's possible to have pr->id as '-1' even when it's actually > + * present in MADT table, e.g. due to limiting dom0 max vcpus > + * less than physical present number. In such case we still want > + * to parse ACPI processor object information, so mimic the > + * pr->id to CPU-0. This should be safe because we only care > + * about raw ACPI information, which only relies on pr->acpi_id. > + * For other information relying on pr->id and gathered through > + * SMP function call, it's safe to let them run on CPU-0 since > + * underlying Xen will collect them. Only a valid pr->id can > + * make later invocations forward progress. > + */ > + pr->id = 0; > + }
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