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Re: [Qemu-devel] [PATCH v2] numa, spapr: align default numa node memory
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH v2] numa, spapr: align default numa node memory size to 256MB |
Date: |
Mon, 20 Mar 2017 16:11:14 -0300 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Mon, Mar 20, 2017 at 03:12:44PM +0100, Laurent Vivier wrote:
> Since commit 224245b ("spapr: Add LMB DR connectors"), NUMA node
> memory size must be aligned to 256MB (SPAPR_MEMORY_BLOCK_SIZE).
>
> But when "-numa" option is provided without "mem" parameter,
> the memory is equally divided between nodes, but 8MB aligned.
> This can be not valid for pseries.
>
> In that case we can have:
> $ ./ppc64-softmmu/qemu-system-ppc64 -m 4G -numa node -numa node -numa node
> qemu-system-ppc64: Node 0 memory size 0x55000000 is not aligned to 256 MiB
>
> With this patch, we have:
> (qemu) info numa
> 3 nodes
> node 0 cpus: 0
> node 0 size: 1280 MB
> node 1 cpus:
> node 1 size: 1280 MB
> node 2 cpus:
> node 2 size: 1536 MB
>
> Signed-off-by: Laurent Vivier <address@hidden>
The code looks good, but a few comments explaining the reason for
the numa_mem_align_shift values would be interesting. Additional
comments below:
> ---
> v2:
> - remove dtc
> - Add a field in MachineClass to only modify the
> numa node memory alignment value for pseries-2.9
> and upper.
>
> hw/core/machine.c | 3 +++
> hw/ppc/spapr.c | 2 ++
> include/hw/boards.h | 1 +
> numa.c | 4 ++--
> 4 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 0d92672..2ad5ab5 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -396,6 +396,9 @@ static void machine_class_init(ObjectClass *oc, void
> *data)
> mc->default_ram_size = 128 * M_BYTE;
> mc->rom_file_has_mr = true;
>
> + /* numa node memory size aligned on 8MB by default */
> + mc->numa_mem_align_shift = 23;
> +
This could include the original "On Linux, each node's border has
to be 8MB aligned" comment from parse_numa_opts(), to explain the
reason for the 8MB default.
> object_class_property_add_str(oc, "accel",
> machine_get_accel, machine_set_accel, &error_abort);
> object_class_property_set_description(oc, "accel",
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 6ee566d..1e72fe8 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3096,6 +3096,7 @@ static void spapr_machine_class_init(ObjectClass *oc,
> void *data)
> xic->ics_resend = spapr_ics_resend;
> xic->icp_get = spapr_icp_get;
> ispc->print_info = spapr_pic_print_info;
> + mc->numa_mem_align_shift = 28;
A comment explaining why spapr requires 256MB alignment would be
nice.
> }
>
> static const TypeInfo spapr_machine_info = {
> @@ -3180,6 +3181,7 @@ static void
> spapr_machine_2_8_class_options(MachineClass *mc)
> {
> spapr_machine_2_9_class_options(mc);
> SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_8);
> + mc->numa_mem_align_shift = 23;
> }
>
> DEFINE_SPAPR_MACHINE(2_8, "2.8", false);
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 269d0ba..31d9c72 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -135,6 +135,7 @@ struct MachineClass {
> bool rom_file_has_mr;
> int minimum_page_bits;
> bool has_hotpluggable_cpus;
> + int numa_mem_align_shift;
>
> HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
> DeviceState *dev);
> diff --git a/numa.c b/numa.c
> index e01cb54..98e4d02 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -338,12 +338,12 @@ void parse_numa_opts(MachineClass *mc)
> if (i == nb_numa_nodes) {
> uint64_t usedmem = 0;
>
> - /* On Linux, each node's border has to be 8MB aligned,
> + /* On Linux, each node's border has to be aligned,
> * the final node gets the rest.
> */
I assume that the 256MB alignment in spapr is not just because of
Linux (is it?). This makes the comment misleading.
I would rewrite it to something like: "Align each node according
to the alignment requirements of the machine class".
> for (i = 0; i < nb_numa_nodes - 1; i++) {
> numa_info[i].node_mem = (ram_size / nb_numa_nodes) &
> - ~((1 << 23UL) - 1);
> + ~((1 << mc->numa_mem_align_shift) -
> 1);
> usedmem += numa_info[i].node_mem;
> }
> numa_info[i].node_mem = ram_size - usedmem;
> --
> 2.9.3
>
--
Eduardo