Re: [PATCH v22 08/20] qapi/s390x/cpu topology: set-cpu-topology qmp command

[Thomas Huth]

On 01/09/2023 17.58, Nina Schoetterl-Glausch wrote:
> From: Pierre Morel <pmorel@linux.ibm.com>
>
> The modification of the CPU attributes are done through a monitor
> command.
>
> It allows to move the core inside the topology tree to optimize
> the cache usage in the case the host's hypervisor previously
> moved the CPU.
>
> The same command allows to modify the CPU attributes modifiers
> like polarization entitlement and the dedicated attribute to notify
> the guest if the host admin modified scheduling or dedication of a vCPU.
>
> With this knowledge the guest has the possibility to optimize the
> usage of the vCPUs.
>
> The command has a feature unstable for the moment.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> Co-developed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> ---
...
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index 52bfbe12a9..c828538f2a 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -23,6 +23,7 @@
>   #include "target/s390x/cpu.h"
>   #include "hw/s390x/s390-virtio-ccw.h"
>   #include "hw/s390x/cpu-topology.h"
> +#include "qapi/qapi-commands-machine-target.h"
>   
>   /*
>    * s390_topology is used to keep the topology information.
> @@ -259,6 +260,29 @@ static bool s390_topology_check(uint16_t socket_id, 
> uint16_t book_id,
>       return true;
>   }
>   
> +/**
> + * s390_topology_need_report
> + * @cpu: Current cpu
> + * @drawer_id: future drawer ID
> + * @book_id: future book ID
> + * @socket_id: future socket ID
> + * @entitlement: future entitlement
> + * @dedicated: future dedicated
> + *
> + * A modified topology change report is needed if the topology
> + * tree or the topology attributes change.
> + */
> +static bool s390_topology_need_report(S390CPU *cpu, int drawer_id,
> +                                   int book_id, int socket_id,
> +                                   uint16_t entitlement, bool dedicated)

Nit: Indentation should match the "(" ?

> +{
> +    return cpu->env.drawer_id != drawer_id ||
> +           cpu->env.book_id != book_id ||
> +           cpu->env.socket_id != socket_id ||
> +           cpu->env.entitlement != entitlement ||
> +           cpu->env.dedicated != dedicated;
> +}
> +
>   /**
>    * s390_update_cpu_props:
>    * @ms: the machine state
> @@ -328,3 +352,114 @@ void s390_topology_setup_cpu(MachineState *ms, S390CPU 
> *cpu, Error **errp)
>       /* topology tree is reflected in props */
>       s390_update_cpu_props(ms, cpu);
>   }
> +
> +static void s390_change_topology(uint16_t core_id,
> +                                 bool has_socket_id, uint16_t socket_id,
> +                                 bool has_book_id, uint16_t book_id,
> +                                 bool has_drawer_id, uint16_t drawer_id,
> +                                 bool has_entitlement,
> +                                 CpuS390Entitlement entitlement,
> +                                 bool has_dedicated, bool dedicated,
> +                                 Error **errp)
> +{
> +    MachineState *ms = current_machine;
> +    int old_socket_entry;
> +    int new_socket_entry;
> +    bool report_needed;
> +    S390CPU *cpu;
> +    ERRP_GUARD();
> +
> +    cpu = s390_cpu_addr2state(core_id);
> +    if (!cpu) {
> +        error_setg(errp, "Core-id %d does not exist!", core_id);
> +        return;
> +    }
> +
> +    /* Get attributes not provided from cpu and verify the new topology */
> +    if (!has_socket_id) {
> +        socket_id = cpu->env.socket_id;
> +    }
> +    if (!has_book_id) {
> +        book_id = cpu->env.book_id;
> +    }
> +    if (!has_drawer_id) {
> +        drawer_id = cpu->env.drawer_id;
> +    }
> +    if (!has_dedicated) {
> +        dedicated = cpu->env.dedicated;
> +    }
> +
> +    /*
> +     * When the user specifies the entitlement as 'auto' on the command line,
> +     * qemu will set the entitlement as:

s/qemu/QEMU/

> +     * Medium when the CPU is not dedicated.
> +     * High when dedicated is true.
> +     */
> +    if (!has_entitlement || (entitlement == S390_CPU_ENTITLEMENT_AUTO)) {

nit: Remove the parentheses around "entitlement == S390_CPU_ENTITLEMENT_AUTO".

> +        if (dedicated) {
> +            entitlement = S390_CPU_ENTITLEMENT_HIGH;
> +        } else {
> +            entitlement = S390_CPU_ENTITLEMENT_MEDIUM;
> +        }
> +    }
> +
> +    if (!s390_topology_check(socket_id, book_id, drawer_id,
> +                             entitlement, dedicated, errp)) {
> +        return;
> +    }
> +
> +    /* Check for space on new socket */
> +    old_socket_entry = s390_socket_nb(cpu);
> +    new_socket_entry = s390_socket_nb_from_ids(drawer_id, book_id, socket_id);
> +
> +    if (new_socket_entry != old_socket_entry) {
> +        if (s390_topology.cores_per_socket[new_socket_entry] >=
> +            ms->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_entry] += 1;
> +        s390_topology.cores_per_socket[old_socket_entry] -= 1;
> +    }
> +
> +    /* Check if we will need to report the modified topology */
> +    report_needed = s390_topology_need_report(cpu, drawer_id, book_id,
> +                                              socket_id, entitlement,
> +                                              dedicated);
> +
> +    /* All checks done, report new topology into the vCPU */
> +    cpu->env.drawer_id = drawer_id;
> +    cpu->env.book_id = book_id;
> +    cpu->env.socket_id = socket_id;
> +    cpu->env.dedicated = dedicated;
> +    cpu->env.entitlement = entitlement;
> +
> +    /* topology tree is reflected in props */
> +    s390_update_cpu_props(ms, cpu);
> +
> +    /* Advertise the topology change */
> +    if (report_needed) {
> +        s390_cpu_topology_set_changed(true);
> +    }
> +}
> +
> +void qmp_set_cpu_topology(uint16_t core,
> +                         bool has_socket, uint16_t socket,
> +                         bool has_book, uint16_t book,
> +                         bool has_drawer, uint16_t drawer,
> +                         bool has_entitlement, CpuS390Entitlement entitlement,
> +                         bool has_dedicated, bool dedicated,
> +                         Error **errp)
> +{
> +    ERRP_GUARD();

No need for ERRP_GUARD here, I think.

> +    if (!s390_has_topology()) {
> +        error_setg(errp, "This machine doesn't support topology");
> +        return;
> +    }
> +
> +    s390_change_topology(core, has_socket, socket, has_book, book,
> +                         has_drawer, drawer, has_entitlement, entitlement,
> +                         has_dedicated, dedicated, errp);
> +}

 Thomas