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

[Corey Ashford <cjashfor@linux.vnet.ibm.com>]

On 1/20/2010 1:35 AM, Andi Kleen wrote:
>> 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.
>

At this point, I don't see a need for that level of detail either.

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

Thanks for the pointer.  I didn't know about the ACPI SLIT and SRAT tables until 
your post.  Having had a quick look at them, I don't think they'd be that 
helpful to us, at least at this point.

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

I think locality could be determined by looking at the device tree.  For 
example, a memory controller for a particular processor chip would be a 
subdirectory of that chip.

>
>> 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.

Good point.

-- 
Regards,

- Corey

Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjashfor@us.ibm.com