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Groups > linux.kernel > #1438500
| From | Joao Martins <joao.m.martins@oracle.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping |
| Date | 2016-07-07 12:20 +0200 |
| Message-ID | <rSezv-5yn-19@gated-at.bofh.it> (permalink) |
| References | (6 earlier) <rPqxc-6tq-27@gated-at.bofh.it> <rPGiB-7LV-13@gated-at.bofh.it> <rPGiB-7LV-11@gated-at.bofh.it> <rRAC6-4FE-33@gated-at.bofh.it> <rRALM-4IW-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 07/05/2016 04:44 PM, Jan Beulich wrote:
>>>> On 05.07.16 at 17:34, <konrad.wilk@oracle.com> wrote:
>> On Thu, Jun 30, 2016 at 03:10:11AM -0600, Jan Beulich wrote:
>>>>>> On 29.06.16 at 18:27, <andrew.cooper3@citrix.com> wrote:
>>>> On 29/06/16 17:19, Vitaly Kuznetsov wrote:
>>>>> To explain better what I'm trying to suggest here please take a look at
>>>>> the attached patch. If we can guarantee long term that ACPI id always
>>>>> equals to Xen's idea of vCPU id this is probably the easiest way.
>>>>>
>>>>> -- Vitaly
>>>>
>>>> The code in hvmloader which sets up the MADT does:
>>>>
>>>> for ( i = 0; i < hvm_info->nr_vcpus; i++ )
>>>> {
>>>> memset(lapic, 0, sizeof(*lapic));
>>>> lapic->type = ACPI_PROCESSOR_LOCAL_APIC;
>>>> lapic->length = sizeof(*lapic);
>>>> /* Processor ID must match processor-object IDs in the DSDT. */
>>>> lapic->acpi_processor_id = i;
>>>> lapic->apic_id = LAPIC_ID(i);
>>>> lapic->flags = (test_bit(i, hvm_info->vcpu_online)
>>>> ? ACPI_LOCAL_APIC_ENABLED : 0);
>>>> lapic++;
>>>> }
>>>>
>>>> So relying on the acpi_processor_id does look to be reliable. That code
>>>> hasn't changed since 2007, and that was only a bugfix. I would go so
>>>> far as to say it is reasonable for us to guarantee this in the guest ABI.
>>>
>>> In fact - is there any other way a guest could learn the vCPU IDs
>>> of its CPUs in a reliable way? I don't think so, and hence this de
>>> facto already is part of the ABI; we should of course spell it out
>>> somewhere.
>>
>> CCing Joao.
>>
>> Joao worked (and I think he posted an RFC patchset?) where this is changed so
>> that the true hardware topology (core, thread, etc) is exposed. This is obviously
>> for cases where you want pinning.
>>
>> I would hesistate to spell this out as an ABI..
>
> Are you perhaps mixing up ACPI and APIC IDs? Here talk is of the
> former, while Joao's patch set was about the latter iirc.
>
Correct, my patch series indeed changed APIC IDs. I guess making acpi_processor_id to
get vcpu_id reliably stated as guest ABI, is safe wrt to future arrangements to apic_ids.
Joao
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[PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-06-28 18:50 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Andrew Cooper <andrew.cooper3@citrix.com> - 2016-06-28 19:30 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-06-29 14:20 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Andrew Cooper <andrew.cooper3@citrix.com> - 2016-06-29 14:40 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-06-29 15:00 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-06-29 18:30 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping "Jan Beulich" <JBeulich@suse.com> - 2016-06-30 11:20 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-07-01 14:10 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping "Jan Beulich" <JBeulich@suse.com> - 2016-07-01 16:00 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2016-07-05 17:40 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping "Jan Beulich" <JBeulich@suse.com> - 2016-07-05 17:50 +0200
Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping Joao Martins <joao.m.martins@oracle.com> - 2016-07-07 12:20 +0200
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