[email protected] writes:
> From: Salil Mehta <[email protected]>
>
> Add support for a new SMP configuration parameter, 'disabledcpus', which
> specifies the number of additional CPUs that are present in the virtual
> machine but administratively disabled at boot. These CPUs are visible in
> firmware (e.g. ACPI tables) yet unavailable to the guest until explicitly
> enabled via QMP/HMP, or via the 'device_set' API (introduced in later
> patches).
>
> This feature is intended for architectures that lack native CPU hotplug
> support but can change the administrative power state of present CPUs.
> It allows simulating CPU hot-add–like scenarios while all CPUs remain
> physically present in the topology at boot time.
>
> Note: ARM is the first architecture to support this concept.
>
> Changes include:
> - Extend CpuTopology with a 'disabledcpus' field.
> - Update machine_parse_smp_config() to account for disabled CPUs when
> computing 'cpus' and 'maxcpus'.
> - Update SMPConfiguration in QAPI to accept 'disabledcpus'.
> - Extend -smp option documentation to describe 'disabledcpus' usage and
> behavior.
>
> Signed-off-by: Salil Mehta <[email protected]>
[...]
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 038eab281c..e45740da33 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1634,6 +1634,8 @@
> #
> # @cpus: number of virtual CPUs in the virtual machine
> #
> +# @disabledcpus: number of additional present but disabled(or offline) CPUs
> +#
> # @maxcpus: maximum number of hotpluggable virtual CPUs in the virtual
> # machine
> #
> @@ -1657,6 +1659,7 @@
> ##
> { 'struct': 'SMPConfiguration', 'data': {
> '*cpus': 'int',
> + '*disabledcpus': 'int',
> '*drawers': 'int',
> '*books': 'int',
> '*sockets': 'int',
We prefer words-with-dashes to wordsruntogether in QAPI/QMP, for
readability: disabled-cpus.
Missing here even before the patch: how these values are related. That
information appears to be buried in machine_parse_smp_config(), which is
160 lines long and with too many conditionals for me to make sense of
now.
> diff --git a/qemu-options.hx b/qemu-options.hx
> index ab23f14d21..83ccde341b 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -326,12 +326,15 @@ SRST
> ERST
>
> DEF("smp", HAS_ARG, QEMU_OPTION_smp,
> - "-smp
> [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets]\n"
> - "
> [,dies=dies][,clusters=clusters][,modules=modules][,cores=cores]\n"
> - " [,threads=threads]\n"
> - " set the number of initial CPUs to 'n' [default=1]\n"
> - " maxcpus= maximum number of total CPUs, including\n"
> - " offline CPUs for hotplug, etc\n"
> + "-smp
> [[cpus=]n][,disabledcpus=disabledcpus][,maxcpus=maxcpus][,drawers=drawers][,books=books]\n"
> + "
> [,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules]\n"
> + " [,cores=cores][,threads=threads]\n"
> + " set the initial number of CPUs present and\n"
> + " administratively enabled at boot time to 'n'
> [default=1]\n"
> + " disabledcpus= number of present but administratively\n"
> + " disabled CPUs (unavailable to the guest at boot)\n"
> + " maxcpus= maximum total CPUs (present + hotpluggable)\n"
> + " on machines without CPU hotplug, defaults to n +
> disabledcpus\n"
> " drawers= number of drawers on the machine board\n"
> " books= number of books in one drawer\n"
> " sockets= number of sockets in one book\n"
> @@ -351,22 +354,49 @@ DEF("smp", HAS_ARG, QEMU_OPTION_smp,
> " For a particular machine type board, an expected CPU topology
> hierarchy\n"
> " can be defined through the supported sub-option. Unsupported
> parameters\n"
> " can also be provided in addition to the sub-option, but their
> values\n"
> - " must be set as 1 in the purpose of correct parsing.\n",
> + " must be set as 1 in the purpose of correct parsing.\n"
> + " \n"
> + " Administratively disabled CPUs: Some machine types do not support
> vCPU\n"
> + " hotplug but their CPUs can be marked disabled (powered off) and
> kept\n"
> + " unavailable to the guest. Later, such CPUs can be enabled via
> QMP/HMP\n"
> + " (e.g., 'device_set ... admin-state=enable'). This is similar to
> hotplug,\n"
> + " except all disabled CPUs are already present at boot. Useful on\n"
> + " architectures that lack architectural CPU hotplug.\n",
> QEMU_ARCH_ALL)
> SRST
> -``-smp
> [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads]``
> - Simulate a SMP system with '\ ``n``\ ' CPUs initially present on
> - the machine type board. On boards supporting CPU hotplug, the optional
> - '\ ``maxcpus``\ ' parameter can be set to enable further CPUs to be
> - added at runtime. When both parameters are omitted, the maximum number
> +``-smp
> [[cpus=]n][,disabledcpus=disabledcpus][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads]``
> + Simulate a SMP system with '\ ``n``\ ' CPUs initially present & enabled
> on
> + the machine type board. Furthermore, on architectures that support
> changing
> + the administrative power state of CPUs, optional '\ ``disabledcpus``\ '
> + parameter specifies *additional* CPUs that are present in firmware (e.g.,
> + ACPI) but are administratively disabled (i.e., not usable by the guest at
> + boot time).
> +
> + This is different from CPU hotplug where additional CPUs are not even
> + present in the system description. Administratively disabled CPUs appear
> in
> + ACPI tables i.e. are provisioned, but cannot be used until explicitly
> + enabled via QMP/HMP or the deviceset API.
> +
> + On boards supporting CPU hotplug, the optional '\ ``maxcpus``\ '
> parameter
> + can be set to enable further CPUs to be added at runtime. When both
> + '\ ``n``\ ' & '\ ``maxcpus``\ ' parameters are omitted, the maximum
> number
> of CPUs will be calculated from the provided topology members and the
> - initial CPU count will match the maximum number. When only one of them
> - is given then the omitted one will be set to its counterpart's value.
> - Both parameters may be specified, but the maximum number of CPUs must
> - be equal to or greater than the initial CPU count. Product of the
> - CPU topology hierarchy must be equal to the maximum number of CPUs.
> - Both parameters are subject to an upper limit that is determined by
> - the specific machine type chosen.
> + initial CPU count will match the maximum number. When only one of them is
> + given then the omitted one will be set to its counterpart's value. Both
> + parameters may be specified, but the maximum number of CPUs must be equal
> + to or greater than the initial CPU count. Product of the CPU topology
> + hierarchy must be equal to the maximum number of CPUs. Both parameters
> are
> + subject to an upper limit that is determined by the specific machine type
> + chosen. Boards that support administratively disabled CPUs but do *not*
> + support CPU hotplug derive the maximum number of CPUs implicitly:
> + '\ ``maxcpus``\ ' is treated as '\ ``n + disabledcpus``\ ' (the total
> CPUs
> + present in firmware). If '\ ``maxcpus``\ ' is provided, it must equal
> + '\ ``n + disabledcpus``\ '. The topology product must equal this derived
> + maximum as well.
> +
> + Note: Administratively disabled CPUs will appear to the guest as
> + unavailable, and any attempt to bring them online must go through QMP/HMP
> + commands like 'device_set'.
>
> To control reporting of CPU topology information, values of the topology
> parameters can be specified. Machines may only support a subset of the
> @@ -425,6 +455,24 @@ SRST
>
> -smp 2
>
> + Examples using 'disabledcpus':
> +
> + For a board without CPU hotplug, enable 4 CPUs at boot and provision
> + 2 additional administratively disabled CPUs (maximum is derived
> + implicitly as 6 = 4 + 2):
> +
> + ::
> +
> + -smp cpus=4,disabledcpus=2
> +
> + For a board that supports CPU hotplug and 'disabledcpus', enable 4 CPUs
> + at boot, provision 2 administratively disabled CPUs, and allow hotplug of
> + 2 more CPUs (for a maximum of 8):
> +
> + ::
> +
> + -smp cpus=4,disabledcpus=2,maxcpus=8
> +
So, maxcpus = cpus + disabledcpus?
Is drawers * books * sockets * dies * clusters * modules * cores *
threads equal or greater than maxcpus?
> Note: The cluster topology will only be generated in ACPI and exposed
> to guest if it's explicitly specified in -smp.
> ERST
> diff --git a/system/vl.c b/system/vl.c
> index 3b7057e6c6..2f0fd21a1f 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -736,6 +736,9 @@ static QemuOptsList qemu_smp_opts = {
> {
> .name = "cpus",
> .type = QEMU_OPT_NUMBER,
> + }, {
> + .name = "disabledcpus",
> + .type = QEMU_OPT_NUMBER,
> }, {
> .name = "drawers",
> .type = QEMU_OPT_NUMBER,
