Re: [PATCH v15 02/11] s390x/cpu topology: add topology entries on CPU hotplug

[Nina Schoetterl-Glausch]

On Wed, 2023-02-01 at 14:20 +0100, Pierre Morel wrote:
> The topology information are attributes of the CPU and are
> specified during the CPU device creation.
> 
> On hot plug we:
> - calculate the default values for the topology for drawers,
>   books and sockets in the case they are not specified.
> - verify the CPU attributes
> - check that we have still room on the desired socket
> 
> The possibility to insert a CPU in a mask is dependent on the
> number of cores allowed in a socket, a book or a drawer, the
> checking is done during the hot plug of the CPU to have an
> immediate answer.
> 
> If the complete topology is not specified, the core is added
> in the physical topology based on its core ID and it gets
> defaults values for the modifier attributes.
> 
> This way, starting QEMU without specifying the topology can
> still get some advantage of the CPU topology.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  include/hw/s390x/cpu-topology.h |  24 +++
>  hw/s390x/cpu-topology.c         | 256 ++++++++++++++++++++++++++++++++
>  hw/s390x/s390-virtio-ccw.c      |  23 ++-
>  hw/s390x/meson.build            |   1 +
>  4 files changed, 302 insertions(+), 2 deletions(-)
>  create mode 100644 hw/s390x/cpu-topology.c
> 
[...]
> 
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> new file mode 100644
> index 0000000000..12df4eca6c
> --- /dev/null
> +++ b/hw/s390x/cpu-topology.c
> @@ -0,0 +1,256 @@
> +/*
> + * CPU Topology
> + *
> + * Copyright IBM Corp. 2022
> + * Author(s): Pierre Morel <pmorel@linux.ibm.com>
> +
> + * This work is licensed under the terms of the GNU GPL, version 2 or (at
> + * your option) any later version. See the COPYING file in the top-level
> + * directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qemu/error-report.h"
> +#include "hw/qdev-properties.h"
> +#include "hw/boards.h"
> +#include "qemu/typedefs.h"
> +#include "target/s390x/cpu.h"
> +#include "hw/s390x/s390-virtio-ccw.h"
> +#include "hw/s390x/cpu-topology.h"
> +
> +/*
> + * s390_topology is used to keep the topology information.
> + * .list: queue the topology entries inside which
> + *        we keep the information on the CPU topology.

.list doesn't exist yet.

> + * .socket: tracks information on the count of cores per socket.
> + * .smp: keeps track of the machine topology.
> + *
> + */
> +S390Topology s390_topology = {
> +    /* will be initialized after the cpu model is realized */
> +    .cores_per_socket = NULL,
> +    .smp = NULL,
> +};
> 
[...]
> +
> +/**
> + * s390_topology_cpu_default:
> + * @cpu: pointer to a S390CPU
> + * @errp: Error pointer
> + *
> + * Setup the default topology for unset attributes.

My suggestion:
Setup the default topology if no attributes are already set.
Passing a CPU with some, but not all, attributes set is considered an error.

> + *
> + * The function accept only all all default values or all set values
> + * for the geometry topology.

acceptS, all all
If you take my suggestion, you can just drop this sentence.

> + *
> + * The function calculates the (drawer_id, book_id, socket_id)
> + * topology by filling the cores starting from the first socket
> + * (0, 0, 0) up to the last (smp->drawers, smp->books, smp->sockets).
> + *
> + * CPU type, polarity and dedication have defaults values set in the
> + * s390x_cpu_properties.
> + */
> +static void s390_topology_cpu_default(S390CPU *cpu, Error **errp)
> +{
> +    CpuTopology *smp = s390_topology.smp;
> +    CPUS390XState *env = &cpu->env;
> +
> +    /* All geometry topology attributes must be set or all unset */
> +    if ((env->socket_id < 0 || env->book_id < 0 || env->drawer_id < 0) &&
> +        (env->socket_id >= 0 || env->book_id >= 0 || env->drawer_id >= 0)) {
> +        error_setg(errp,
> +                   "Please define all or none of the topology geometry 
> attributes");
> +        return;
> +    }
> +
> +    /* Check if one of the geometry topology is unset */
> +    if (env->socket_id < 0) {
> +        /* Calculate default geometry topology attributes */
> +        env->socket_id = (env->core_id / smp->cores) % smp->sockets;
> +        env->book_id = (env->core_id / (smp->sockets * smp->cores)) %
> +                       smp->books;
> +        env->drawer_id = (env->core_id /
> +                          (smp->books * smp->sockets * smp->cores)) %
> +                         smp->drawers;
> +    }
> +}
> 
[...]
> +
> +/**
> + * s390_set_core_in_socket:
> + * @cpu: the new S390CPU to insert in the topology structure
> + * @drawer_id: new drawer_id
> + * @book_id: new book_id
> + * @socket_id: new socket_id
> + * @creation: if is true the CPU is a new CPU and there is no old socket
> + *            to handle.
> + *            if is false, this is a moving the CPU and old socket count
> + *            must be decremented.
> + * @errp: the error pointer
> + *
> + */
> +static void s390_set_core_in_socket(S390CPU *cpu, int drawer_id, int book_id,

Maybe name it s390_(topology_)?add_core_to_socket instead.

> +                                    int socket_id, bool creation, Error 
> **errp)
> +{
> +    int old_socket = s390_socket_nb(cpu);
> +    int new_socket;
> +
> +    if (creation) {
> +        new_socket = old_socket;
> +    } else {

You need parentheses here.

> +        new_socket = drawer_id * s390_topology.smp->books +
                       (
> +                     book_id * s390_topology.smp->sockets +
                               )
> +                     socket_id;
> +    }
> +
> +    /* Check for space on new socket */
> +    if ((new_socket != old_socket) &&
> +        (s390_topology.cores_per_socket[new_socket] >=
> +         s390_topology.smp->cores)) {
> +        error_setg(errp, "No more space on this socket");
> +        return;
> +    }
> +
> +    /* Update the count of cores in sockets */
> +    s390_topology.cores_per_socket[new_socket] += 1;
> +    if (!creation) {
> +        s390_topology.cores_per_socket[old_socket] -= 1;
> +    }
> +}
> 
[...]

> +/**
> + * s390_topology_set_cpu:
> + * @ms: MachineState used to initialize the topology structure on
> + *      first call.
> + * @cpu: the new S390CPU to insert in the topology structure
> + * @errp: the error pointer
> + *
> + * Called from CPU Hotplug to check and setup the CPU attributes
> + * before to insert the CPU in the topology.
> + */
> +void s390_topology_set_cpu(MachineState *ms, S390CPU *cpu, Error **errp)

The name is rather non informative.
s390_topology_setup_cpu ?

> +{
> +    ERRP_GUARD();
> +
> +    /*
> +     * We do not want to initialize the topology if the cpu model
> +     * does not support topology consequently, we have to wait for
                                   ^
Still think there should be a comma here.

> +     * the first CPU to be realized, which realizes the CPU model
> +     * to initialize the topology structures.
> +     *
> +     * s390_topology_set_cpu() is called from the cpu hotplug.
> +     */
> +    if (!s390_topology.cores_per_socket) {
> +        s390_topology_init(ms);
> +    }
> +
> +    s390_topology_check(cpu, errp);
> +    if (*errp) {
> +        return;
> +    }
> +
> +    /* Set the CPU inside the socket */
> +    s390_set_core_in_socket(cpu, 0, 0, 0, true, errp);
> +    if (*errp) {
> +        return;
> +    }
> +
> +    /* topology tree is reflected in props */
> +    s390_update_cpu_props(ms, cpu);
> +}
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index f3cc845d3b..9bc51a83f4 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -44,6 +44,7 @@
>  #include "hw/s390x/pv.h"
>  #include "migration/blocker.h"
>  #include "qapi/visitor.h"
> +#include "hw/s390x/cpu-topology.h"
>  
>  static Error *pv_mig_blocker;
>  
> @@ -310,10 +311,18 @@ static void s390_cpu_plug(HotplugHandler *hotplug_dev,
>  {
>      MachineState *ms = MACHINE(hotplug_dev);
>      S390CPU *cpu = S390_CPU(dev);
> +    ERRP_GUARD();
>  
>      g_assert(!ms->possible_cpus->cpus[cpu->env.core_id].cpu);
>      ms->possible_cpus->cpus[cpu->env.core_id].cpu = OBJECT(dev);
>  
> +    if (s390_has_topology()) {
> +        s390_topology_set_cpu(ms, cpu, errp);
> +        if (*errp) {
> +            return;
> +        }
> +    }
> +
>      if (dev->hotplugged) {
>          raise_irq_cpu_hotplug();
>      }
> @@ -551,11 +560,21 @@ static const CPUArchIdList 
> *s390_possible_cpu_arch_ids(MachineState *ms)
>                                    sizeof(CPUArchId) * max_cpus);
>      ms->possible_cpus->len = max_cpus;
>      for (i = 0; i < ms->possible_cpus->len; i++) {
> +        CpuInstanceProperties *props = &ms->possible_cpus->cpus[i].props;
> +
>          ms->possible_cpus->cpus[i].type = ms->cpu_type;
>          ms->possible_cpus->cpus[i].vcpus_count = 1;
>          ms->possible_cpus->cpus[i].arch_id = i;
> -        ms->possible_cpus->cpus[i].props.has_core_id = true;
> -        ms->possible_cpus->cpus[i].props.core_id = i;
> +
> +        props->has_core_id = true;
> +        props->core_id = i;
> +        props->has_socket_id = true;
> +        props->socket_id = i / ms->smp.cores;
> +        props->has_book_id = true;
> +        props->book_id = i / (ms->smp.cores * ms->smp.sockets);
> +        props->has_drawer_id = true;
> +        props->drawer_id = i /
> +                           (ms->smp.cores * ms->smp.sockets * ms->smp.books);

You need to calculate the modulus like in s390_topology_cpu_default, right?

>      }
>  
>      return ms->possible_cpus;
> diff --git a/hw/s390x/meson.build b/hw/s390x/meson.build
> index f291016fee..58dfbdff4f 100644
> --- a/hw/s390x/meson.build
> +++ b/hw/s390x/meson.build
> @@ -24,6 +24,7 @@ s390x_ss.add(when: 'CONFIG_KVM', if_true: files(
>    's390-stattrib-kvm.c',
>    'pv.c',
>    's390-pci-kvm.c',
> +  'cpu-topology.c',
>  ))
>  s390x_ss.add(when: 'CONFIG_TCG', if_true: files(
>    'tod-tcg.c',