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

[Dave Hansen]

On 12/4/18 6:13 PM, Jerome Glisse wrote:
> On Tue, Dec 04, 2018 at 05:06:49PM -0800, Dave Hansen wrote:
>> OK, but there are 1024*1024 matrix cells on a systems with 1024
>> proximity domains (ACPI term for NUMA node).  So it sounds like you are
>> proposing a million-directory approach.
> 
> No, pseudo code:
>     struct list links;
> 
>     for (unsigned r = 0; r < nrows; r++) {
>         for (unsigned c = 0; c < ncolumns; c++) {
>             if (!link_find(links, hmat[r][c].bandwidth,
>                            hmat[r][c].latency)) {
>                 link = link_new(hmat[r][c].bandwidth,
>                                 hmat[r][c].latency);
>                 // add initiator and target correspond to that row
>                 // and columns to this new link
>                 list_add(&link, links);
>             }
>         }
>     }
> 
> So all cells that have same property are under the same link. 

OK, so the "link" here is like a cable.  It's like saying, "we have a
network and everything is connected with an ethernet cable that can do
1gbit/sec".

But, what actually connects an initiator to a target?  I assume we still
need to know which link is used for each target/initiator pair.  Where
is that enumerated?

I think this just means we need a million symlinks to a "link" instead
of a million link directories.  Still not great.

> Note that userspace can parse all this once during its initialization
> and create pools of target to use.

It sounds like you're agreeing that there is too much data in this
interface for applications to _regularly_ parse it.  We need some
central thing that parses it all and caches the results.