Re: [RFC PATCH 00/14] Heterogeneous Memory System (HMS) and hbind()

[Dave Hansen <dave.hansen@intel.com>]

On 12/6/18 12:11 PM, Logan Gunthorpe wrote:
>> My concern with having folks do per-program parsing, *and* having a huge
>> amount of data to parse makes it unusable.  The largest systems will
>> literally have hundreds of thousands of objects in /sysfs, even in a
>> single directory.  That makes readdir() basically impossible, and makes
>> even open() (if you already know the path you want somehow) hard to do fast.
> Is this actually realistic? I find it hard to imagine an actual hardware
> bus that can have even thousands of devices under a single node, let
> alone hundreds of thousands.

Jerome's proposal, as I understand it, would have generic "links".
They're not an instance of bus, but characterize a class of "link".  For
instance, a "link" might characterize the characteristics of the QPI bus
between two CPU sockets. The link directory would enumerate the list of
all *instances* of that link

So, a "link" directory for QPI would say Socket0<->Socket1,
Socket1<->Socket2, Socket1<->Socket2, Socket2<->PCIe-1.2.3.4 etc...  It
would have to enumerate the connections between every entity that shared
those link properties.

While there might not be millions of buses, there could be millions of
*paths* across all those buses, and that's what the HMAT describes, at
least: the net result of all those paths.