On 2018-12-06 4:09 p.m., Dave Hansen wrote: > This looks great. But, we don't _have_ this kind of information for any > system that I know about or any system available in the near future. > > We basically have two different world views: > 1. The system is described point-to-point. A connects to B @ > 100GB/s. B connects to C at 50GB/s. Thus, C->A should be > 50GB/s. > * Less information to convey > * Potentially less precise if the properties are not perfectly > additive. If A->B=10ns and B->C=20ns, A->C might be >30ns. > * Costs must be calculated instead of being explicitly specified > 2. The system is described endpoint-to-endpoint. A->B @ 100GB/s > B->C @ 50GB/s, A->C @ 50GB/s. > * A *lot* more information to convey O(N^2)? > * Potentially more precise. > * Costs are explicitly specified, not calculated > > These patches are really tied to world view #1. But, the HMAT is really > tied to world view #1. I didn't think this was meant to describe actual real world performance between all of the links. If that's the case all of this seems like a pipe dream to me. Attributes like cache coherency, atomics, etc should fit well in world view #1... and, at best, some kind of flag saying whether or not to use a particular link if you care about transfer speed. -- But we don't need special "link" directories to describe the properties of existing buses. You're not *really* going to know bandwidth or latency for any of this unless you actually measure it on the system in question. Logan
