Re: [PATCH v12 2/7] s390x/cpu topology: reporting the CPU topology to the guest

[Pierre Morel]

On 12/6/22 10:48, Janis Schoetterl-Glausch wrote:
> On Tue, 2022-11-29 at 18:42 +0100, Pierre Morel wrote:
> > The guest uses the STSI instruction to get information on the
> > CPU topology.
> >
> > Let us implement the STSI instruction for the basis CPU topology
> > level, level 2.
> >
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > ---
> >   target/s390x/cpu.h          |  77 +++++++++++++++
> >   hw/s390x/s390-virtio-ccw.c  |  12 +--
> >   target/s390x/cpu_topology.c | 186 ++++++++++++++++++++++++++++++++++++
> >   target/s390x/kvm/kvm.c      |   6 +-
> >   target/s390x/meson.build    |   1 +
> >   5 files changed, 274 insertions(+), 8 deletions(-)
> >   create mode 100644 target/s390x/cpu_topology.c
> >
> > diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> > index 7d6d01325b..dd878ac916 100644
> > --- a/target/s390x/cpu.h
> > +++ b/target/s390x/cpu.h
> [...]
>
> > +/* Configuration topology */
> > +typedef struct SysIB_151x {
> > +    uint8_t  reserved0[2];
> > +    uint16_t length;
> > +    uint8_t  mag[S390_TOPOLOGY_MAG];
> > +    uint8_t  reserved1;
> > +    uint8_t  mnest;
> > +    uint32_t reserved2;
> > +    char tle[0];
>
> AFAIK [] is preferred over [0].

grr, yes, I think I have been already told so :)


> > +} QEMU_PACKED QEMU_ALIGNED(8) SysIB_151x;
> > +QEMU_BUILD_BUG_ON(sizeof(SysIB_151x) != 16);
>
> [...]
> > +/*
> > + * s390_topology_add_cpu:
> > + * @topo: pointer to the topology
> > + * @cpu : pointer to the new CPU
> > + *
> > + * The topology pointed by S390CPU, gives us the CPU topology
> > + * established by the -smp QEMU aruments.
> > + * The core-id is used to calculate the position of the CPU inside
> > + * the topology:
> > + *  - the socket, container TLE, containing the CPU, we have one socket
> > + *    for every num_cores cores.
> > + *  - the CPU TLE inside the socket, we have potentionly up to 4 CPU TLE
> > + *    in a container TLE with the assumption that all CPU are identical
> > + *    with the same polarity and entitlement because we have maximum 256
> > + *    CPUs and each TLE can hold up to 64 identical CPUs.
> > + *  - the bit in the 64 bit CPU TLE core mask
> > + */
> > +static void s390_topology_add_cpu(S390Topology *topo, S390CPU *cpu)
> > +{
> > +    int core_id = cpu->env.core_id;
> > +    int bit, origin;
> > +    int socket_id;
> > +
> > +    cpu->machine_data = topo;
> > +    socket_id = core_id / topo->num_cores;
> > +    /*
> > +     * At the core level, each CPU is represented by a bit in a 64bit
> > +     * uint64_t 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.
> > +     */
>
> This comment still contains redundant sentences.
> Did you have a look at my suggestion in v10 patch 1?

Yes, I had, and sorry, I forgot to report here inside the patch 11.
I will take it, thanks for it.

> > +    bit = core_id;
> > +    origin = bit / 64;
> > +    bit %= 64;
> > +    bit = 63 - bit;
> > +
> > +    topo->socket[socket_id].active_count++;
> > +    set_bit(bit, &topo->socket[socket_id].mask[origin]);
> > +}
> > +
> > +/*
> > + * s390_prepare_topology:
> > + * @s390ms : pointer to the S390CcwMachite State
> > + *
> > + * Calls s390_topology_add_cpu to organize the topology
> > + * inside the topology device before writing the SYSIB.
> > + *
> > + * The topology is currently fixed on boot and do not change
>
> does not change

yes, thanks


regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen