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

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 06, 2015 at 01:53:05PM +0530, Bharata B Rao wrote:
> 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) ?

That seems a bit nasty, since then the granularity of adding blocks
will be enormous for small guests as well.

Is it possible to increase the maximum size of a single DIMM, but not
the minimum?  That way you can still do small inserts for small
guests.  To get the full RAM for big guests youd have to insert big
chunks though, due to the limited number of slots.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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