Re: [PATCH v15 08/11] qapi/s390x/cpu topology: x-set-cpu-topology monitor command

[Pierre Morel <pmorel@linux.ibm.com>]

On 2/8/23 19:40, Nina Schoetterl-Glausch wrote:
> On Wed, 2023-02-01 at 14:20 +0100, Pierre Morel wrote:
>> The modification of the CPU attributes are done through a monitor
>> command.
>>
>> It allows to move the core inside the topology tree to optimise
>> 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 is made experimental for the moment.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> ---
>>   qapi/machine-target.json | 29 +++++++++++++
>>   include/monitor/hmp.h    |  1 +
>>   hw/s390x/cpu-topology.c  | 88 ++++++++++++++++++++++++++++++++++++++++
>>   hmp-commands.hx          | 16 ++++++++
>>   4 files changed, 134 insertions(+)
>>
>> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
>> index 2e267fa458..58df0f5061 100644
>> --- a/qapi/machine-target.json
>> +++ b/qapi/machine-target.json
>> @@ -342,3 +342,32 @@
>>                      'TARGET_S390X',
>>                      'TARGET_MIPS',
>>                      'TARGET_LOONGARCH64' ] } }
>> +
>> +##
>> +# @x-set-cpu-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
> 
> I wonder if it wouldn't be more convenient for the caller if everything is optional.

Yes, it is a good point.

> 
>> +# @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': 'x-set-cpu-topology',
>> +  'data': {
>> +      'core': 'int',
>> +      'socket': 'int',
>> +      'book': 'int',
>> +      'drawer': 'int',
> 
> Did you consider naming those core-id, etc.? It would be consistent with
> query-cpus-fast/CpuInstanceProperties. Also all your variables end with _id.
> I don't care really just wanted to point it out.

OK, core-id etc. looks better

> 
>> +      '*polarity': 'int',
>> +      '*dedicated': 'bool'
>> +  },
>> +  'if': { 'all': [ 'TARGET_S390X', 'CONFIG_KVM' ] }
>> +}
> 
> So apparently this is the old way of doing an experimental api.
> 
>> Names beginning with ``x-`` used to signify "experimental".  This
>> convention has been replaced by special feature "unstable".
> 
>> Feature "unstable" marks a command, event, enum value, or struct
>> member as unstable.  It is not supported elsewhere so far.  Interfaces
>> so marked may be withdrawn or changed incompatibly in future releases.

OK

> 
>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>> index 1b3bdcb446..12827479cf 100644
>> --- a/include/monitor/hmp.h
>> +++ b/include/monitor/hmp.h
>> @@ -151,5 +151,6 @@ 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_x_set_cpu_topology(Monitor *mon, const QDict *qdict);
>>   
>>   #endif
>> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
>> index c33378577b..6c50050991 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.
>> @@ -379,3 +383,87 @@ void s390_topology_set_cpu(MachineState *ms, S390CPU *cpu, Error **errp)
>>       /* topology tree is reflected in props */
>>       s390_update_cpu_props(ms, cpu);
>>   }
>> +
>> +/*
>> + * qmp and hmp implementations
>> + */
>> +
>> +static void s390_change_topology(int64_t core_id, int64_t socket_id,
>> +                                 int64_t book_id, int64_t drawer_id,
>> +                                 int64_t polarity, bool dedicated,
>> +                                 Error **errp)
>> +{
>> +    MachineState *ms = current_machine;
>> +    S390CPU *cpu;
>> +    ERRP_GUARD();
>> +
>> +    cpu = (S390CPU *)ms->possible_cpus->cpus[core_id].cpu;
>> +    if (!cpu) {
>> +        error_setg(errp, "Core-id %ld does not exist!", core_id);
>> +        return;
>> +    }
>> +
>> +    /* Verify the new topology */
>> +    s390_topology_check(cpu, errp);
>> +    if (*errp) {
>> +        return;
>> +    }
>> +
>> +    /* Move the CPU into its new socket */
>> +    s390_set_core_in_socket(cpu, drawer_id, book_id, socket_id, true, errp);
> 
> The cpu isn't being created, so that should be false instead of true, right?

Yes right, should be "false"

> 
>> +
>> +    /* All checks done, report topology in environment */
>> +    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 = polarity;
>> +
>> +    /* topology tree is reflected in props */
>> +    s390_update_cpu_props(ms, cpu);
>> +
>> +    /* Advertise the topology change */
>> +    s390_cpu_topology_set_modified();
>> +}
>> +
>> +void qmp_x_set_cpu_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)
>> +{
>> +    ERRP_GUARD();
>> +
>> +    if (!s390_has_topology()) {
>> +        error_setg(errp, "This machine doesn't support topology");
>> +        return;
>> +    }
>> +    if (!has_polarity) {
>> +        polarity = POLARITY_VERTICAL_MEDIUM;
>> +    }
>> +    if (!has_dedicated) {
>> +        dedicated = false;
>> +    }
>> +    s390_change_topology(core, socket, book, drawer, polarity, dedicated, errp);
>> +}
>> +
>> +void hmp_x_set_cpu_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_x_set_cpu_topology(core, socket, book, drawer,
>> +                           has_polarity, polarity,
>> +                           has_dedicated, dedicated,
>> +                           &local_err);
>> +    if (hmp_handle_error(mon, local_err)) {
>> +        return;
>> +    }
> 
> What is the if for? The function ends anyway.

Right, I take it away.
Thanks.

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen