Re: [Qemu-devel] [RFC PATCH v3 12/24] spapr: CPU hotplug support

[Thomas Huth <thuth@redhat.com>]

On Fri, 24 Apr 2015 12:17:34 +0530
Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:

> Support CPU hotplug via device-add command. Set up device tree
> entries for the hotplugged CPU core and use the exising EPOW event
> infrastructure to send CPU hotplug notification to the guest.
> 
> Also support cold plugged CPUs that are specified by -device option
> on cmdline.
> 
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c        | 129 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/ppc/spapr_events.c |   8 ++--
>  hw/ppc/spapr_rtas.c   |  11 +++++
>  3 files changed, 145 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index b526b7d..9b0701c 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
[...]
> +static void spapr_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> +                            Error **errp)
> +{
> +    CPUState *cs = CPU(dev);
> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> +    int id = ppc_get_vcpu_dt_id(cpu);
> +    sPAPRDRConnector *drc =
> +        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> +    sPAPRDRConnectorClass *drck;
> +    int smt = kvmppc_smt_threads();
> +    Error *local_err = NULL;
> +    void *fdt = NULL;
> +    int i, fdt_offset = 0;
> +
> +    /* Set NUMA node for the added CPUs  */
> +    for (i = 0; i < nb_numa_nodes; i++) {
> +        if (test_bit(cs->cpu_index, numa_info[i].node_cpu)) {
> +            cs->numa_node = i;
> +            break;
> +        }
> +    }
> +
> +    /*
> +     * SMT threads return from here, only main thread (core) will
> +     * continue and signal hotplug event to the guest.
> +     */
> +    if ((id % smt) != 0) {
> +        return;
> +    }
> +
> +    if (!spapr->dr_cpu_enabled) {
> +        /*
> +         * This is a cold plugged CPU but the machine doesn't support
> +         * DR. So skip the hotplug path ensuring that the CPU is brought
> +         * up online with out an associated DR connector.
> +         */
> +        return;
> +    }
> +
> +    g_assert(drc);
> +
> +    /*
> +     * Setup CPU DT entries only for hotplugged CPUs. For boot time or
> +     * coldplugged CPUs DT entries are setup in spapr_finalize_fdt().
> +     */
> +    if (dev->hotplugged) {
> +        fdt = spapr_populate_hotplug_cpu_dt(dev, cs, &fdt_offset);
> +    }
> +
> +    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> +    drck->attach(drc, dev, fdt, fdt_offset, !dev->hotplugged, &local_err);
> +    if (local_err) {
> +        g_free(fdt);
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    /*
> +     * We send hotplug notification interrupt to the guest only in case
> +     * of hotplugged CPUs.
> +     */
> +    if (dev->hotplugged) {
> +        spapr_hotplug_req_add_event(drc);
> +    } else {
> +        /*
> +         * HACK to support removal of hotplugged CPU after VM migration:
> +         *
> +         * Since we want to be able to hot-remove those coldplugged CPUs
> +         * started at boot time using -device option at the target VM, we set
> +         * the right allocation_state and isolation_state for them, which for
> +         * the hotplugged CPUs would be set via RTAS calls done from the
> +         * guest during hotplug.
> +         *
> +         * This allows the coldplugged CPUs started using -device option to
> +         * have the right isolation and allocation states as expected by the
> +         * CPU hot removal code.
> +         *
> +         * This hack will be removed once we have DRC states migrated as part
> +         * of VM migration.
> +         */
> +        drck->set_allocation_state(drc, SPAPR_DR_ALLOCATION_STATE_USABLE);
> +        drck->set_isolation_state(drc, SPAPR_DR_ISOLATION_STATE_UNISOLATED);
> +    }
> +
> +    return;

Cosmetic nit: Superfluous return statement

> +}
> +
[...]
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 57ec97a..48aeb86 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -121,6 +121,16 @@ static void rtas_query_cpu_stopped_state(PowerPCCPU *cpu_,
>      rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
>  }
>  
> +static void spapr_cpu_set_endianness(PowerPCCPU *cpu)
> +{
> +    PowerPCCPU *fcpu = POWERPC_CPU(first_cpu);
> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(fcpu);
> +
> +    if (!(*pcc->interrupts_big_endian)(fcpu)) {

Functions pointers are sometimes still confusing to me, but can't you
simplify that to:

    if (!pcc->interrupts_big_endian(fcpu)) {

?

> +        cpu->env.spr[SPR_LPCR] |= LPCR_ILE;
> +    }
> +}

 Thomas