Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

On Wed, Dec 27, 2017 at 10:10:34AM +0100, Brice Goglin wrote:

quoted

Perhaps we can enlist /proc/iomem or a similar enumeration interface
to tell userspace the NUMA node and whether the kernel thinks it has
better or worse performance characteristics relative to base
system-RAM, i.e. new IORES_DESC_* values. I'm worried that if we start
publishing absolute numbers in sysfs userspace will default to looking
for specific magic numbers in sysfs vs asking the kernel for memory
that has performance characteristics relative to base "System RAM". In
other words the absolute performance information that the HMAT
publishes is useful to the kernel, but it's not clear that userspace
needs that vs a relative indicator for making NUMA node preference
decisions.

Some HPC users will benchmark the machine to discovery actual
performance numbers anyway.
However, most users won't do this. They will want to know relative
performance of different nodes. If you normalize HMAT values by dividing
them with system-RAM values, that's likely OK. If you just say "that
node is faster than system RAM", it's not precise enough.

So "this memory has 800% bandwidth of normal" and "this memory has 70%
bandwidth of normal"?