Re: [PATCH v14 08/11] qapi/s390/cpu topology: change-topology monitor command

[Nina Schoetterl-Glausch]

On Thu, 2023-01-05 at 15:53 +0100, Pierre Morel wrote:
> The modification of the CPU attributes are done through a monitor
> commands.
> 
> It allows to move the core inside the topology tree to optimise
> the cache usage in the case the host's hypervizor previously
> moved the CPU.
> 
> The same command allows to modifiy 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.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  qapi/machine-target.json |  29 ++++++++
>  include/monitor/hmp.h    |   1 +
>  hw/s390x/cpu-topology.c  | 141 +++++++++++++++++++++++++++++++++++++++
>  hmp-commands.hx          |  16 +++++
>  4 files changed, 187 insertions(+)
> 
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index 2e267fa458..75b0aa254d 100644
> --- a/qapi/machine-target.json
> +++ b/qapi/machine-target.json
> @@ -342,3 +342,32 @@
>                     'TARGET_S390X',
>                     'TARGET_MIPS',
>                     'TARGET_LOONGARCH64' ] } }
> +
> +##
> +# @change-topology:
> +#
> +# @core: the vCPU ID to be moved
> +# @socket: the destination socket where to move the vCPU
> +# @book: the destination book where to move the vCPU
> +# @drawer: the destination drawer where to move the vCPU
> +# @polarity: optional polarity, default is last polarity set by the guest
> +# @dedicated: optional, if the vCPU is dedicated to a real CPU
> +#
> +# Modifies the topology by moving the CPU inside the topology
> +# tree or by changing a modifier attribute of a CPU.
> +#
> +# Returns: Nothing on success, the reason on failure.
> +#
> +# Since: <next qemu stable release, eg. 1.0>
> +##
> +{ 'command': 'change-topology',
> +  'data': {
> +      'core': 'int',
> +      'socket': 'int',
> +      'book': 'int',
> +      'drawer': 'int',
> +      '*polarity': 'int',
> +      '*dedicated': 'bool'
> +  },
> +  'if': { 'all': [ 'TARGET_S390X', 'CONFIG_KVM' ] }
> +}
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index 27f86399f7..15c36bf549 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -144,5 +144,6 @@ void hmp_human_readable_text_helper(Monitor *mon,
>                                      HumanReadableText *(*qmp_handler)(Error 
> **));
>  void hmp_info_stats(Monitor *mon, const QDict *qdict);
>  void hmp_pcie_aer_inject_error(Monitor *mon, const QDict *qdict);
> +void hmp_change_topology(Monitor *mon, const QDict *qdict);
>  
>  #endif
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index b69955a1cd..0faffe657e 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -18,6 +18,10 @@
>  #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"
> +#include "qapi/qmp/qdict.h"
> +#include "monitor/hmp.h"
> +#include "monitor/monitor.h"
>  
>  /*
>   * s390_topology is used to keep the topology information.
> @@ -203,6 +207,21 @@ static void s390_topology_set_entry(S390TopologyEntry 
> *entry,
>      s390_topology.sockets[s390_socket_nb(id)]++;
>  }
>  
> +/**
> + * s390_topology_clear_entry:
> + * @entry: Topology entry to setup
> + * @id: topology id to use for the setup
> + *
> + * Clear the core bit inside the topology mask and
> + * decrements the number of cores for the socket.
> + */
> +static void s390_topology_clear_entry(S390TopologyEntry *entry,
> +                                      s390_topology_id id)
> +{
> +    clear_bit(63 - id.core, &entry->mask);

This doesn't take the origin into account.

> +    s390_topology.sockets[s390_socket_nb(id)]--;

I suppose this function cannot run concurrently, so the same CPU doesn't get 
removed twice.

> +}
> +
>  /**
>   * s390_topology_new_entry:
>   * @id: s390_topology_id to add
> @@ -383,3 +402,125 @@ void s390_topology_set_cpu(MachineState *ms, S390CPU 
> *cpu, Error **errp)
>  
>      s390_topology_insert(id);
>  }
> +
> +/*
> + * qmp and hmp implementations
> + */
> +
> +static S390TopologyEntry *s390_topology_core_to_entry(int core)
> +{
> +    S390TopologyEntry *entry;
> +
> +    QTAILQ_FOREACH(entry, &s390_topology.list, next) {
> +        if (entry->mask & (1UL << (63 - core))) {

origin here also.

> +            return entry;
> +        }
> +    }
> +    return NULL;

This should not return NULL unless the core id is invalid.
Might be better to validate that somewhere else.

> +}
> +
> +static void s390_change_topology(Error **errp, int64_t core, int64_t socket,
> +                                 int64_t book, int64_t drawer,
> +                                 int64_t polarity, bool dedicated)
> +{
> +    S390TopologyEntry *entry;
> +    s390_topology_id new_id;
> +    s390_topology_id old_id;
> +    Error *local_error = NULL;

I think you could use ERRP_GUARD here also.
> +
> +    /* Get the old entry */
> +    entry = s390_topology_core_to_entry(core);
> +    if (!entry) {
> +        error_setg(errp, "No core %ld", core);
> +        return;
> +    }
> +
> +    /* Compute old topology id */
> +    old_id = entry->id;
> +    old_id.core = core;
> +
> +    /* Compute new topology id */
> +    new_id = entry->id;
> +    new_id.core = core;
> +    new_id.socket = socket;
> +    new_id.book = book;
> +    new_id.drawer = drawer;
> +    new_id.p = polarity;
> +    new_id.d = dedicated;
> +    new_id.type = S390_TOPOLOGY_CPU_IFL;
> +
> +    /* Same topology entry, nothing to do */
> +    if (entry->id.id == new_id.id) {
> +        return;
> +    }
> +
> +    /* Check for space on the socket if ids are different */
> +    if ((s390_socket_nb(old_id) != s390_socket_nb(new_id)) &&
> +        (s390_topology.sockets[s390_socket_nb(new_id)] >=
> +         s390_topology.smp->sockets)) {
> +        error_setg(errp, "No more space on this socket");
> +        return;
> +    }
> +
> +    /* Verify the new topology */
> +    s390_topology_check(&local_error, new_id);
> +    if (local_error) {
> +        error_propagate(errp, local_error);
> +        return;
> +    }
> +
> +    /* Clear the old topology */
> +    s390_topology_clear_entry(entry, old_id);
> +
> +    /* Insert the new topology */
> +    s390_topology_insert(new_id);
> +
> +    /* Remove unused entry */
> +    if (!entry->mask) {
> +        QTAILQ_REMOVE(&s390_topology.list, entry, next);
> +        g_free(entry);
> +    }
> +
> +    /* Advertise the topology change */
> +    s390_cpu_topology_set();
> +}
> +
> +void qmp_change_topology(int64_t core, int64_t socket,
> +                         int64_t book, int64_t drawer,
> +                         bool has_polarity, int64_t polarity,
> +                         bool has_dedicated, bool dedicated,
> +                         Error **errp)
> +{
> +    Error *local_err = NULL;
> +
> +    if (!s390_has_topology()) {
> +        error_setg(&local_err, "This machine doesn't support topology");
> +        return;
> +    }

Do you really want to ignore has_polarity and has_dedicated here?
What happens in this case?

> +    s390_change_topology(&local_err, core, socket, book, drawer,
> +                         polarity, dedicated);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +    }
> +}
> +
> +void hmp_change_topology(Monitor *mon, const QDict *qdict)
> +{
> +    const int64_t core = qdict_get_int(qdict, "core");
> +    const int64_t socket = qdict_get_int(qdict, "socket");
> +    const int64_t book = qdict_get_int(qdict, "book");
> +    const int64_t drawer = qdict_get_int(qdict, "drawer");
> +    bool has_polarity    = qdict_haskey(qdict, "polarity");
> +    const int64_t polarity = qdict_get_try_int(qdict, "polarity", 0);
> +    bool has_dedicated    = qdict_haskey(qdict, "dedicated");
> +    const bool dedicated = qdict_get_try_bool(qdict, "dedicated", false);
> +    Error *local_err = NULL;
> +
> +    qmp_change_topology(core, socket, book, drawer,
> +                        has_polarity, polarity,
> +                        has_dedicated, dedicated,
> +                        &local_err);
> +    if (hmp_handle_error(mon, local_err)) {
> +        return;
> +    }
> +}
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 673e39a697..a617cfed0d 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1815,3 +1815,19 @@ SRST
>    Dump the FDT in dtb format to *filename*.
>  ERST
>  #endif
> +
> +#if defined(TARGET_S390X) && defined(CONFIG_KVM)
> +    {
> +        .name       = "change-topology",
> +        .args_type  = 
> "core:l,socket:l,book:l,drawer:l,polarity:l?,dedicated:b?",
> +        .params     = "core socket book drawer [polarity] [dedicated]",
> +        .help       = "Move CPU 'core' to 'socket/book/drawer' "
> +                      "optionaly modifies polarity and dedication",
> +        .cmd        = hmp_change_topology,
> +    },
> +
> +SRST
> +``change-topology`` *core* *socket* *book* *drawer* *polarity* *dedicated*
> +  Moves the CPU  *core* to *socket* *book* *drawer* with *polarity* 
> *dedicated*.
> +ERST
> +#endif