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

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Message-ID: <20100120093555.GA24355@basil.fritz.box>
Date:	Wed, 20 Jan 2010 10:35:55 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...glemail.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	Philip Mucci <mucci@...s.utk.edu>,
	Maynard Johnson <mpjohn@...ibm.com>, Carl Love <cel@...ibm.com>
Subject: Re: [RFC] perf_events: support for uncore a.k.a. nest units

> 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.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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