Re: [RFC] perf_events: support for uncore a.k.a. nest units

From: Andi Kleen
Date: Wed Jan 20 2010 - 04:36:14 EST

> Yes, I agree. Also it's easy to construct a system design that doesn't
> have a hierarchical topology. A simple example would be a cluster of 32
> nodes, each of which is connected to its 31 neighbors. Perhaps for the

I doubt it's needed or useful to describe all details of an interconnect.

If detailed distance information is needed a simple table like
the SLIT table exported by ACPI would seem easier to handle.

But at least some degree of locality (e.g. "local memory controller")
would make sense.

> purposes of just enumerating PMUs, a tree might be sufficient, but it's not
> clear to me that it is mathematically sufficient for all topologies, not to
> mention if it's intuitive enough to use. For example,
> highly-interconnected components might require that PMU leaf nodes be
> duplicated in multiple branches, i.e. PMU paths might not be unique in some
> topologies.

We already have cyclical graphs in sysfs using symlinks. I'm not
sure they are all that easy to parse/handle, but at least they
can be described.


ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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