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

[Pierre Morel]

On 2/2/23 17:42, Nina Schoetterl-Glausch wrote:
> 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.

right, I move it to the corresponding patch.

> > + * .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.

Thanks, I take your suggestion.

> > + *
> > + * 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.

OK, it is better

> > +                                    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;

If you prefer I can us parentheses.


> > +    }
> > +
> > +    /* 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 ?

OK

> > +{
> > +    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.

OK

> > +     * 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?

!!! yes of course, good catch, I forgot that.

Since there are two uses of this calculation, what about using inlines?
like:

static inline int s390_std_socket(int n, CpuTopology *smp)
{
    return (n / smp->cores) % smp->sockets;
}

static inline int s390_std_book(int n, CpuTopology *smp)
{
    return (n / (smp->cores * smp->sockets)) % smp->books;
}

static inline int s390_std_drawer(int n, CpuTopology *smp)
{
    return (n / (smp->cores * smp->sockets * smp->books)) % smp->books;
}


Thanks for the comments.

Regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen