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

[Brice Goglin <brice.goglin@gmail.com>]

Le 30/12/2017 à 07:58, Matthew Wilcox a écrit :
> On Wed, Dec 27, 2017 at 10:10:34AM +0100, Brice Goglin wrote:
>>> 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"?

I guess that would work.
Brice