Re: [PATCH v10 1/9] s390x/cpu topology: core_id sets s390x CPU topology

[Cédric Le Goater]

Hello Pierre,

On 10/12/22 18:20, Pierre Morel wrote:
> In the S390x CPU topology the core_id specifies the CPU address
> and the position of the core withing the topology.
>
> Let's build the topology based on the core_id.
> s390x/cpu topology: core_id sets s390x CPU topology
>
> In the S390x CPU topology the core_id specifies the CPU address
> and the position of the cpu withing the topology.
>
> Let's build the topology based on the core_id.

The commit log is doubled.

> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>   include/hw/s390x/cpu-topology.h |  45 +++++++++++
>   hw/s390x/cpu-topology.c         | 132 ++++++++++++++++++++++++++++++++
>   hw/s390x/s390-virtio-ccw.c      |  21 +++++
>   hw/s390x/meson.build            |   1 +
>   4 files changed, 199 insertions(+)
>   create mode 100644 include/hw/s390x/cpu-topology.h
>   create mode 100644 hw/s390x/cpu-topology.c
>
> diff --git a/include/hw/s390x/cpu-topology.h b/include/hw/s390x/cpu-topology.h
> new file mode 100644
> index 0000000000..66c171d0bc
> --- /dev/null
> +++ b/include/hw/s390x/cpu-topology.h
> @@ -0,0 +1,45 @@
> +/*
> + * CPU Topology
> + *
> + * Copyright 2022 IBM Corp.
> + *
> + * 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.
> + */
> +#ifndef HW_S390X_CPU_TOPOLOGY_H
> +#define HW_S390X_CPU_TOPOLOGY_H
> +
> +#include "hw/qdev-core.h"
> +#include "qom/object.h"
> +
> +typedef struct S390TopoContainer {
> +    int active_count;
> +} S390TopoContainer;

This structure does not seem very useful.

> +
> +#define S390_TOPOLOGY_CPU_IFL 0x03
> +#define S390_TOPOLOGY_MAX_ORIGIN ((63 + S390_MAX_CPUS) / 64)
> +typedef struct S390TopoTLE { 

The 'Topo' is redundant as TLE stands for 'topology-list entry'. This is minor.

> +    uint64_t mask[S390_TOPOLOGY_MAX_ORIGIN];
> +} S390TopoTLE;
> +
> +struct S390Topology {
> +    SysBusDevice parent_obj;
> +    int cpus;
> +    S390TopoContainer *socket;
> +    S390TopoTLE *tle;
> +    MachineState *ms;

hmm, it would be cleaner to introduce the fields and properties needed
by the S390Topology model and avoid dragging the machine object pointer.
AFAICT, these properties would be :

  "nr-cpus"
  "max-cpus"
  "nr-sockets"



> +};
> +
> +#define TYPE_S390_CPU_TOPOLOGY "s390-topology"
> +OBJECT_DECLARE_SIMPLE_TYPE(S390Topology, S390_CPU_TOPOLOGY)
> +
> +S390Topology *s390_get_topology(void);
> +void s390_topology_new_cpu(int core_id);
> +
> +static inline bool s390_has_topology(void)
> +{
> +    return false;
> +}
> +
> +#endif
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> new file mode 100644
> index 0000000000..42b22a1831
> --- /dev/null
> +++ b/hw/s390x/cpu-topology.c
> @@ -0,0 +1,132 @@
> +/*
> + * CPU Topology
> + *
> + * Copyright IBM Corp. 2022

The Copyright tag is different in the .h file.
 
> + * 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/sysbus.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"
> +
> +S390Topology *s390_get_topology(void)
> +{
> +    static S390Topology *s390Topology;
> +
> +    if (!s390Topology) {
> +        s390Topology = S390_CPU_TOPOLOGY(
> +            object_resolve_path(TYPE_S390_CPU_TOPOLOGY, NULL));
> +    }
> +
> +    return s390Topology;

I am not convinced this routine is useful. The s390Topology pointer
could be stored under the machine state I think. It wouldn't be a
problem when CPUs are hot plugged since we have access to the machine
in the hot plug handler.

For the stsi call, 'struct ArchCPU' probably lacks a back pointer to
the machine objects with which CPU interact. These are typically
interrupt controllers or this new s390Topology model. You could add
the pointer there or, better, under a generic 'void *opaque' attribute.

That said, what you did works fine. The modeling could be cleaner.

> +}
> +
> +/*
> + * s390_topology_new_cpu:
> + * @core_id: the core ID is machine wide
> + *
> + * The topology returned by s390_get_topology(), gives us the CPU
> + * topology established by the -smp QEMU aruments.
> + * The core-id gives:
> + *  - the Container TLE (Topology List Entry) containing the CPU TLE.
> + *  - in the CPU TLE the origin, or offset of the first bit in the core mask
> + *  - the bit in the CPU TLE core mask
> + */
> +void s390_topology_new_cpu(int core_id)
> +{
> +    S390Topology *topo = s390_get_topology();
> +    int socket_id;
> +    int bit, origin;
> +
> +    /* In the case no Topology is used nothing is to be done here */
> +    if (!topo) {
> +        return;
> +    }

I would move this test in the caller.

> +
> +    socket_id = core_id / topo->cpus;
> +
> +    /*
> +     * At the core level, each CPU is represented by a bit in a 64bit
> +     * unsigned long which represent the presence of a CPU.
> +     * The firmware assume that all CPU in a CPU TLE have the same
> +     * type, polarization and are all dedicated or shared.
> +     * In that case the origin variable represents the offset of the first
> +     * CPU in the CPU container.
> +     * More than 64 CPUs per socket are represented in several CPU containers
> +     * inside the socket container.
> +     * The only reason to have several S390TopologyCores inside a socket is
> +     * to have more than 64 CPUs.
> +     * In that case the origin variable represents the offset of the first CPU
> +     * in the CPU container. More than 64 CPUs per socket are represented in
> +     * several CPU containers inside the socket container.
> +     */
> +    bit = core_id;
> +    origin = bit / 64;
> +    bit %= 64;
> +    bit = 63 - bit;
> +
> +    topo->socket[socket_id].active_count++;
> +    set_bit(bit, &topo->tle[socket_id].mask[origin]);

here, the tle array is indexed with a socket id and ...

> +}
> +
> +/**
> + * s390_topology_realize:
> + * @dev: the device state
> + * @errp: the error pointer (not used)
> + *
> + * During realize the machine CPU topology is initialized with the
> + * QEMU -smp parameters.
> + * The maximum count of CPU TLE in the all Topology can not be greater
> + * than the maximum CPUs.
> + */
> +static void s390_topology_realize(DeviceState *dev, Error **errp)
> +{
> +    MachineState *ms = MACHINE(qdev_get_machine());
> +    S390Topology *topo = S390_CPU_TOPOLOGY(dev);
> +
> +    topo->cpus = ms->smp.cores * ms->smp.threads;> +
> +    topo->socket = g_new0(S390TopoContainer, ms->smp.sockets);
> +    topo->tle = g_new0(S390TopoTLE, ms->smp.max_cpus);


... here, the tle array is allocated with max_cpus and this looks
weird. I will dig the specs to try to understand.

> +
> +    topo->ms = ms;

See comment above regarding the properties.

> +}
> +
> +/**
> + * topology_class_init:
> + * @oc: Object class
> + * @data: (not used)
> + *
> + * A very simple object we will need for reset and migration.
> + */
> +static void topology_class_init(ObjectClass *oc, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(oc);
> +
> +    dc->realize = s390_topology_realize;
> +    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> +}
> +
> +static const TypeInfo cpu_topology_info = {
> +    .name          = TYPE_S390_CPU_TOPOLOGY,
> +    .parent        = TYPE_SYS_BUS_DEVICE,
> +    .instance_size = sizeof(S390Topology),
> +    .class_init    = topology_class_init,
> +};
> +
> +static void topology_register(void)
> +{
> +    type_register_static(&cpu_topology_info);
> +}
> +type_init(topology_register);
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 03855c7231..aa99a62e42 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -43,6 +43,7 @@
>   #include "sysemu/sysemu.h"
>   #include "hw/s390x/pv.h"
>   #include "migration/blocker.h"
> +#include "hw/s390x/cpu-topology.h"
>   
>   static Error *pv_mig_blocker;
>   
> @@ -94,6 +95,18 @@ static void s390_init_cpus(MachineState *machine)
>       }
>   }
>   
> +static void s390_init_topology(MachineState *machine)
> +{
> +    DeviceState *dev;
> +
> +    if (s390_has_topology()) {
> +        dev = qdev_new(TYPE_S390_CPU_TOPOLOGY);
> +        object_property_add_child(&machine->parent_obj,
> +                                  TYPE_S390_CPU_TOPOLOGY, OBJECT(dev));
> +        sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> +    }
> +}
> +
>   static const char *const reset_dev_types[] = {
>       TYPE_VIRTUAL_CSS_BRIDGE,
>       "s390-sclp-event-facility",
> @@ -244,6 +257,9 @@ static void ccw_init(MachineState *machine)
>       /* init memory + setup max page size. Required for the CPU model */
>       s390_memory_init(machine->ram);
>   
> +    /* Adding the topology must be done before CPU intialization */

initialization

> +    s390_init_topology(machine);
> +
>       /* init CPUs (incl. CPU model) early so s390_has_feature() works */
>       s390_init_cpus(machine);
>   
> @@ -306,6 +322,11 @@ static void s390_cpu_plug(HotplugHandler *hotplug_dev,
>       g_assert(!ms->possible_cpus->cpus[cpu->env.core_id].cpu);
>       ms->possible_cpus->cpus[cpu->env.core_id].cpu = OBJECT(dev);
>   
> +    /* Inserting the CPU in the Topology can not fail */
> +    if (s390_has_topology()) {
> +        s390_topology_new_cpu(cpu->env.core_id);
> +    }
> +
>       if (dev->hotplugged) {
>           raise_irq_cpu_hotplug();
>       }
> diff --git a/hw/s390x/meson.build b/hw/s390x/meson.build
> index f291016fee..653f6ab488 100644
> --- a/hw/s390x/meson.build
> +++ b/hw/s390x/meson.build
> @@ -2,6 +2,7 @@ s390x_ss = ss.source_set()
>   s390x_ss.add(files(
>     'ap-bridge.c',
>     'ap-device.c',
> +  'cpu-topology.c',
>     'ccw-device.c',
>     'css-bridge.c',
>     'css.c',