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RE: [Question] Regarding presence of duplicate ACPI CPU entries at two n
From: |
Salil Mehta |
Subject: |
RE: [Question] Regarding presence of duplicate ACPI CPU entries at two nodes \\_SB.CXXX and \\_SB.CPUS.CXXX of namespace |
Date: |
Wed, 29 Jan 2020 12:23:22 +0000 |
Please ignore this!
> From: Linuxarm [mailto:address@hidden] On Behalf Of Salil Mehta
> Sent: Wednesday, January 29, 2020 11:51 AM
> To: address@hidden; address@hidden
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; Linuxarm <address@hidden>; address@hidden;
> pbonzini <address@hidden>; Igor Mammedov <address@hidden>;
> address@hidden
> Subject: [Question] Regarding presence of duplicate ACPI CPU entries at two
> nodes
> \\_SB.CXXX and \\_SB.CPUS.CXXX of namespace
>
> Hello,
>
> Observation:
> If we launch Linux Guest VM using QEMU(running on any type host. I am using
> x86)
> with
> CPU based on any ARM64 architecture then I could see QEMU populating ACPI
> nodes
> related to same CPU at 2 places of the ACPI namespace:
> 1. \\_SB.CXXX
> 2. \\_SB.CPUS.CXXX
>
> Above results in Guest VM showing duplicate CPU entries in the sysfs for the
> same CPUS.
> I could make out the entries under \\_SB.CPUS.XXX are part of the container.
>
> estuary:/$ ls -al /sys/bus/acpi/devices/
>
> Observation 1: (belongs to \\_SB.C00X)
> ACPI0007:00 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:00
> ACPI0007:01 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:01
> ACPI0007:02 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:02
> ACPI0007:03 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:03
> ACPI0007:04 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:04
> ACPI0007:05 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:05
>
> Observation 2: (belongs to \\_SB.CPUS.C00X and under container ACPI0010:00
> part
> of \\_SB.CPUS)
> ACPI0007:06
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:06
> ACPI0007:07
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:07
> ACPI0007:08
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:08
> ACPI0007:09
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:09
> ACPI0007:0a
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:0a
> ACPI0007:0b
> -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:0b
> ACPI0010:00 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00
>
>
> estuary:/$ cat /sys/bus/acpi/devices/ACPI0010\:00/path
> \_SB_.CPUS
>
> estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:00/uid
> 0
> estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:00/path
> \_SB_.C000
>
> estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:06/uid
> 0
> estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:06/path
> \_SB_.CPUS.C000
>
>
>
> QEMU Code Excerpt:
> I could trace with in QEMU AML code, the CPUS are being appended at 2 places:
>
>
> Code 1. File: hw/arm/virt-acpi-build.c (Cause of Observation 1 i.e.
> \\_SB.CXXX )
>
> static void acpi_dsdt_add_cpus(Aml *scope, int smp_cpus)
> {
> uint16_t i;
>
> for (i = 0; i < smp_cpus; i++) { --->{should be possible cpus anyways}
> Aml *dev = aml_device("C%.03X", i);
> aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
> aml_append(dev, aml_name_decl("_UID", aml_int(i)));
> aml_append(scope, dev);
> }
> }
>
>
> Code 2. File: hw/acpi/cpu.c (Cause of Observation 2 i.e. \\_SB.CPUS.CXXX)
>
> void build_cpus_aml(..)
> {
> [...]
> cpus_dev = aml_device("\\_SB.CPUS");
> {
> [...]
> /* build Processor object for each processor */
> for (i = 0; i < arch_ids->len; i++) {
> Aml *dev;
> Aml *uid = aml_int(i);
> GArray *madt_buf = g_array_new(0, 1, 1);
> int arch_id = arch_ids->cpus[i].arch_id;
>
> if (opts.acpi_1_compatible && arch_id < 255) {
> dev = aml_processor(i, 0, 0, CPU_NAME_FMT, i);
> } else {
> dev = aml_device(CPU_NAME_FMT, i);
> aml_append(dev, aml_name_decl("_HID",
> aml_string("ACPI0007")));
> aml_append(dev, aml_name_decl("_UID", uid));
> }
> [...]
> }
> [...]
> }
>
>
>
> Questions:
> Q1. I could not understand the purpose of keeping acpi_dsdt_add_cpus() after
> the code 2.
> was introduced as part of the below change and which is already adding
> CPUS
> related
> AML to \\_SB.CPUS namespace?
>
> acpi: cpuhp: add CPU devices AML with _STA method
> commit 5e1b5d93887b52eede156f846b6c4c5c8bbcfcdb
>
> Q2. Do we really require CPUs being added by acpi_dsdt_add_cpus() in
> \\_SB.CXXX
> Namespace OR is it a stray code left?
>
>
>
> Please help to correct if there is a gap in my understanding here and please
> forgive me if I have terribly missed out something very basic here.
>
> Many thanks!
>
> Best Regards
> Salil
>