Re: [Qemu-devel] [RFC PATCH v3 21/24] spapr: Initialize hotplug memory address space

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Tue, May 05, 2015 at 10:48:50AM +0200, Igor Mammedov wrote:
> On Fri, 24 Apr 2015 12:17:43 +0530
> Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:
> 
> > Initialize a hotplug memory region under which all the hotplugged
> > memory is accommodated. Also enable memory hotplug by setting
> > CONFIG_MEM_HOTPLUG.
> > 
> > Modelled on i386 memory hotplug.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > ---
> >  default-configs/ppc64-softmmu.mak |  1 +
> >  hw/ppc/spapr.c                    | 38 ++++++++++++++++++++++++++++++++++++++
> >  include/hw/ppc/spapr.h            | 12 ++++++++++++
> >  3 files changed, 51 insertions(+)
> > 
> > diff --git a/default-configs/ppc64-softmmu.mak b/default-configs/ppc64-softmmu.mak
> > index 22ef132..16b3011 100644
> > --- a/default-configs/ppc64-softmmu.mak
> > +++ b/default-configs/ppc64-softmmu.mak
> > @@ -51,3 +51,4 @@ CONFIG_XICS_KVM=$(and $(CONFIG_PSERIES),$(CONFIG_KVM))
> >  # For PReP
> >  CONFIG_MC146818RTC=y
> >  CONFIG_ISA_TESTDEV=y
> > +CONFIG_MEM_HOTPLUG=y
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 910a50f..9dc4c36 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -125,6 +125,9 @@ struct sPAPRMachineState {
> >  
> >      /*< public >*/
> >      char *kvm_type;
> > +    ram_addr_t hotplug_memory_base;
> > +    MemoryRegion hotplug_memory;
> > +    bool enforce_aligned_dimm;
> >  };
> >  
> >  sPAPREnvironment *spapr;
> > @@ -1514,6 +1517,7 @@ static void ppc_spapr_init(MachineState *machine)
> >      QemuOpts *opts = qemu_opts_find(qemu_find_opts("smp-opts"), NULL);
> >      int sockets = opts ? qemu_opt_get_number(opts, "sockets", 0) : 0;
> >      int cores = (smp_cpus/smp_threads) ? smp_cpus/smp_threads : 1;
> > +    sPAPRMachineState *ms = SPAPR_MACHINE(machine);
> >  
> >      sockets = sockets ? sockets : cores;
> >      msi_supported = true;
> > @@ -1613,6 +1617,36 @@ static void ppc_spapr_init(MachineState *machine)
> >          memory_region_add_subregion(sysmem, 0, rma_region);
> >      }
> >  
> > +    /* initialize hotplug memory address space */
> > +    if (machine->ram_size < machine->maxram_size) {
> > +        ram_addr_t hotplug_mem_size =
> > +            machine->maxram_size - machine->ram_size;
> > +
> > +        if (machine->ram_slots > SPAPR_MAX_RAM_SLOTS) {
> > +            error_report("unsupported amount of memory slots: %"PRIu64,
> > +                         machine->ram_slots);
> > +            exit(EXIT_FAILURE);
> > +        }
> > +
> > +        ms->hotplug_memory_base = ROUND_UP(machine->ram_size,
> > +                                    SPAPR_HOTPLUG_MEM_ALIGN);
> > +
> > +        if (ms->enforce_aligned_dimm) {
> > +            hotplug_mem_size += SPAPR_HOTPLUG_MEM_ALIGN * machine->ram_slots;
> > +        }
> > +
> > +        if ((ms->hotplug_memory_base + hotplug_mem_size) < hotplug_mem_size) {
> > +            error_report("unsupported amount of maximum memory: " RAM_ADDR_FMT,
> > +                         machine->maxram_size);
> > +            exit(EXIT_FAILURE);
> > +        }
> > +
> > +        memory_region_init(&ms->hotplug_memory, OBJECT(ms),
> > +                           "hotplug-memory", hotplug_mem_size);
> > +        memory_region_add_subregion(sysmem, ms->hotplug_memory_base,
> > +                                    &ms->hotplug_memory);
> > +    }
> > +
> >      filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, "spapr-rtas.bin");
> >      spapr->rtas_size = get_image_size(filename);
> >      spapr->rtas_blob = g_malloc(spapr->rtas_size);
> > @@ -1844,11 +1878,15 @@ static void spapr_set_kvm_type(Object *obj, const char *value, Error **errp)
> >  
> >  static void spapr_machine_initfn(Object *obj)
> >  {
> > +    sPAPRMachineState *ms = SPAPR_MACHINE(obj);
> > +
> >      object_property_add_str(obj, "kvm-type",
> >                              spapr_get_kvm_type, spapr_set_kvm_type, NULL);
> >      object_property_set_description(obj, "kvm-type",
> >                                      "Specifies the KVM virtualization mode (HV, PR)",
> >                                      NULL);
> > +
> > +    ms->enforce_aligned_dimm = true;
> >  }
> >  
> >  static void ppc_cpu_do_nmi_on_cpu(void *arg)
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index ecac6e3..53560e9 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -542,6 +542,18 @@ struct sPAPREventLogEntry {
> >  
> >  #define SPAPR_MEMORY_BLOCK_SIZE (1 << 28) /* 256MB */
> >  
> > +/*
> > + * This defines the maximum number of DIMM slots we can have for sPAPR
> > + * guest. This is not defined by sPAPR but we are defining it to 4096 slots
> > + * here. With the worst case addition of SPAPR_MEMORY_BLOCK_SIZE
> > + * (256MB) memory per slot, we should be able to support 1TB of guest
> > + * hotpluggable memory.
> > + */
> > +#define SPAPR_MAX_RAM_SLOTS     (1ULL << 12)
> why not write 4096 instead of (1ULL << 12), much easier to read.

Sure.

> 
> BTW:
> KVM supports upto 509 memory slots including slots consumed by
> initial memory.

I see that PowerPC defaults to 32 slots. So having 4096 slots is really
pointless then ? So to ensure more hot-pluggable memory space is available
should I be increasing the size of the minimum pluggable memory in a
dimm slot (as defined by SPAPR_MEMORY_BLOCK_SIZE above) ?

Regards,
Bharata.