Re: [PATCH v4 1/4] memblock tests: add simulation of physical memory with multiple NUMA nodes

[David Hildenbrand]

On 07.09.22 01:43, Rebecca Mckeever wrote:
> On Tue, Sep 06, 2022 at 03:17:46PM +0200, David Hildenbrand wrote:
> > On 04.09.22 06:21, Rebecca Mckeever wrote:
> > > Add function setup_numa_memblock() for setting up a memory layout with
> > > multiple NUMA nodes in a previously allocated dummy physical memory.
> > > This function can be used in place of setup_memblock() in tests that need
> > > to simulate a NUMA system.
> > >
> > > setup_numa_memblock():
> > > - allows for setting up a memory layout by specifying the fraction of
> > >     MEM_SIZE in each node
> > >
> > > Set CONFIG_NODES_SHIFT to 4 when building with NUMA=1 to allow for up to
> > > 16 NUMA nodes.
> > >
> > > Signed-off-by: Rebecca Mckeever <remckee0@xxxxxxxxx>
> > > ---
> > >    .../testing/memblock/scripts/Makefile.include |  2 +-
> > >    tools/testing/memblock/tests/common.c         | 29 +++++++++++++++++++
> > >    tools/testing/memblock/tests/common.h         |  4 ++-
> > >    3 files changed, 33 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tools/testing/memblock/scripts/Makefile.include b/tools/testing/memblock/scripts/Makefile.include
> > > index aa6d82d56a23..998281723590 100644
> > > --- a/tools/testing/memblock/scripts/Makefile.include
> > > +++ b/tools/testing/memblock/scripts/Makefile.include
> > > @@ -3,7 +3,7 @@
> > >    # Simulate CONFIG_NUMA=y
> > >    ifeq ($(NUMA), 1)
> > > -	CFLAGS += -D CONFIG_NUMA
> > > +	CFLAGS += -D CONFIG_NUMA -D CONFIG_NODES_SHIFT=4
> > >    endif
> > >    # Use 32 bit physical addresses.
> > > diff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c
> > > index eec6901081af..b6110df21b2a 100644
> > > --- a/tools/testing/memblock/tests/common.c
> > > +++ b/tools/testing/memblock/tests/common.c
> > > @@ -72,6 +72,35 @@ void setup_memblock(void)
> > >    	fill_memblock();
> > >    }
> > > +/**
> > > + * setup_numa_memblock:
> > > + * Set up a memory layout with multiple NUMA nodes in a previously allocated
> > > + * dummy physical memory.
> > > + * @nodes: an array containing the denominators of the fractions of MEM_SIZE
> > > + *         contained in each node (e.g., if nodes[0] = SZ_8, node 0 will
> > > + *         contain 1/8th of MEM_SIZE)
> > > + *
> > > + * The nids will be set to 0 through NUMA_NODES - 1.
> > > + */
> > > +void setup_numa_memblock(const phys_addr_t nodes[])
> > > +{
> > > +	phys_addr_t base;
> > > +	int flags;
> > > +
> > > +	reset_memblock_regions();
> > > +	base = (phys_addr_t)memory_block.base;
> > > +	flags = (movable_node_is_enabled()) ? MEMBLOCK_NONE : MEMBLOCK_HOTPLUG;
> > > +
> > > +	for (int i = 0; i < NUMA_NODES; i++) {
> > > +		assert(nodes[i] <= MEM_SIZE && nodes[i] > 0);
> >
> > I think it would be even easier to get if this would just be a fraction.
> > E.g., instead of "1/8 * MEM_SIZE" just "1/8". All values have to add up to
> > 1.
> >
> > ... but then we'd have to mess with floats eventually, so I guess this makes
> > it easier to handle these fractions.
> >
> >
> > We could use "int" and simply specify the fraction in percent, like
> >
> > nodes[0] = 50;
> > nodes[1] = 25;
> > nodes[2] = 25;
> >
> > and everything has to add up to 100.
> This would still be a float for 1/8th (12.5) and 1/16th (6.25). What if
> it was the "percent" of 256 (i.e., 0x100)?

Right, or in something "smaller" like 1/32 th. I don't think we go below 
that?

If we don't need more digits, why not in "basis points" (per ten thousand)
-> https://en.wikipedia.org/wiki/Basis_point

nodes[0] = 5000; /* 1/2  */
nodes[1] = 2500; /* 1/4 */
nodes[2] = 1250; /* 1/8 */
nodes[4] = 0625; /* 1/32 */
nodes[5] = 0625;


> > > +		phys_addr_t size = MEM_SIZE / nodes[i];
> >
> >
> > Hmmm, assuming a single node with "MEM_SIZE", we would get size=1.
> For a single node of MEM_SIZE, nodes[0] would be 1.
>
> > Shouldn't this be "size = nodes[i]"
> >
> > ?
> No, not with the current implementation. The nodes array stores the
> denominator of the fraction that will be multiplied by MEM_SIZE to
> determine the size of that node (the numerator is always 1). So if the
> size of the node should be 1/8 * MEM_SIZE, the nodes array just stores
> the 8. I think the name of the array is misleading. Do you have any
> suggestions for a better name?

Then I am confused about the
	assert(nodes[i] <= MEM_SIZE && nodes[i] > 0);

assertion :)

I think it would really be best to just store the actual fraction 
somehow. But maybe just I am confused :)

--
Thanks,

David / dhildenb