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 <lviv...@redhat.com>
> ---
> 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.
> +
> 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
> --
> 2.9.3
>
--
Eduardo
