Re: [Qemu-devel] [PATCH v2 2/2] numa, spapr: equally distribute memory on nodes

[David Gibson]

On Thu, Apr 27, 2017 at 05:31:48PM -0300, Eduardo Habkost wrote:
> On Thu, Apr 27, 2017 at 12:12:59PM +0200, Laurent Vivier wrote:
> > When there are more nodes than memory available to put the minimum
> > allowed memory by node, all the memory is put on the last node.
> > 
> > This is because we put (ram_size / nb_numa_nodes) &
> > ~((1 << mc->numa_mem_align_shift) - 1); on each node, and in this
> > case the value is 0. This is particularly true with pseries,
> > as the memory must be aligned to 256MB.
> > 
> > To avoid this problem, this patch uses an error diffusion algorithm [1]
> > to distribute equally the memory on nodes.
> > 
> > Example:
> > 
> > qemu-system-ppc64 -S -nographic  -nodefaults -monitor stdio -m 1G -smp 8 \
> >                   -numa node -numa node -numa node \
> >                   -numa node -numa node -numa node
> > 
> > Before:
> > 
> > (qemu) info numa
> > 6 nodes
> > node 0 cpus: 0 6
> > node 0 size: 0 MB
> > node 1 cpus: 1 7
> > node 1 size: 0 MB
> > node 2 cpus: 2
> > node 2 size: 0 MB
> > node 3 cpus: 3
> > node 3 size: 0 MB
> > node 4 cpus: 4
> > node 4 size: 0 MB
> > node 5 cpus: 5
> > node 5 size: 1024 MB
> > 
> > After:
> > (qemu) info numa
> > 6 nodes
> > node 0 cpus: 0 6
> > node 0 size: 0 MB
> > node 1 cpus: 1 7
> > node 1 size: 256 MB
> > node 2 cpus: 2
> > node 2 size: 0 MB
> > node 3 cpus: 3
> > node 3 size: 256 MB
> > node 4 cpus: 4
> > node 4 size: 256 MB
> > node 5 cpus: 5
> > node 5 size: 256 MB
> > 
> > [1] https://en.wikipedia.org/wiki/Error_diffusion
> > 
> > Signed-off-by: Laurent Vivier <address@hidden>
> > ---
> >  hw/ppc/spapr.c         | 21 ++++++++++++++++++++-
> >  include/hw/ppc/spapr.h |  3 ++-
> >  2 files changed, 22 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 80d12d0..be498e2 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -3106,6 +3106,23 @@ static void 
> > spapr_pic_print_info(InterruptStatsProvider *obj,
> >      ics_pic_print_info(spapr->ics, mon);
> >  }
> >  
> > +static void spapr_numa_auto_assign_ram(uint64_t *nodes, int nb_nodes,
> > +                                       ram_addr_t size)
> > +{
> > +    int i;
> > +    uint64_t usedmem = 0, node_mem;
> > +    uint64_t granularity = size / nb_nodes;
> > +    uint64_t propagate = 0;
> > +
> > +    for (i = 0; i < nb_nodes - 1; i++) {
> > +        node_mem = (granularity + propagate) & ~(SPAPR_MEMORY_BLOCK_SIZE - 
> > 1);
> > +        propagate = granularity + propagate - node_mem;
> > +        nodes[i] = node_mem;
> > +        usedmem += node_mem;
> > +    }
> > +    nodes[i] = ram_size - usedmem;
> > +}
> 
> This new algorithm is a much better default, I would like to
> enable it for all machines by default. We could move it to
> core/machine.c:machine_class_init(), and set numa_auto_assign_ram
> to NULL on pc-*-2.9 and spapr-2.9.

Right.  So, the convention that the default is the new behaviour and
we override to set the older behaviour on previous machine types is
strong enough that I think we should keep it here, even though it adds
some complications.

Note that it might be simpler not to have a "NULL" behaviour.  Instead
the core code can provide both old style and error diffusion versions
of the assign hook.  Set it to the error difusion one in the base
MachineClass, then override it to the old one in previous versioned
machine types (basically just the previous pc and spapr models,
AFAIK).

> 
> > +
> >  static void spapr_machine_class_init(ObjectClass *oc, void *data)
> >  {
> >      MachineClass *mc = MACHINE_CLASS(oc);
> > @@ -3162,7 +3179,8 @@ static void spapr_machine_class_init(ObjectClass *oc, 
> > void *data)
> >       * SPAPR_MEMORY_BLOCK_SIZE (256M) since that's the granularity
> >       * in which LMBs are represented and hot-added
> >       */
> > -    mc->numa_mem_align_shift = 28;
> > +    mc->numa_mem_align_shift = SPAPR_MEMORY_BLOCK_SIZE_SHIFT;
> > +    mc->numa_auto_assign_ram = spapr_numa_auto_assign_ram;
> >  }
> >  
> >  static const TypeInfo spapr_machine_info = {
> > @@ -3242,6 +3260,7 @@ static void 
> > spapr_machine_2_9_class_options(MachineClass *mc)
> >  {
> >      spapr_machine_2_10_class_options(mc);
> >      SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_9);
> > +    mc->numa_auto_assign_ram = NULL;
> >  }
> >  
> >  DEFINE_SPAPR_MACHINE(2_9, "2.9", false);
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index 5802f88..8f4a588 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -653,7 +653,8 @@ int spapr_rtc_import_offset(sPAPRRTCState *rtc, int64_t 
> > legacy_offset);
> >  
> >  int spapr_rng_populate_dt(void *fdt);
> >  
> > -#define SPAPR_MEMORY_BLOCK_SIZE (1 << 28) /* 256MB */
> > +#define SPAPR_MEMORY_BLOCK_SIZE_SHIFT 28 /* 256MB */
> > +#define SPAPR_MEMORY_BLOCK_SIZE (1 << SPAPR_MEMORY_BLOCK_SIZE_SHIFT)
> >  
> >  /*
> >   * This defines the maximum number of DIMM slots we can have for sPAPR
> 

-- 
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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