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Subject: Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs
From: Peter Zijlstra <peterz@infradead.org>
To: Corey Ashford <cjashfor@linux.vnet.ibm.com>
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Date: Tue, 11 May 2010 08:50:16 +0200
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On Mon, 2010-05-10 at 16:54 -0700, Corey Ashford wrote:
> 
> Just to give a concrete example, the IBM Wire-Speed Processor has four
> AT-"nodes" per chip, each containing four PowerPC cores.
> 
> Those four nodes together share a number of nest PMU accelerators, I/O
> devices, buses etc. which each have their own PMUs.  Further adding to
> the structure is that some of the nodes are replicated.  For example,
> we have two memory controllers, each with a pair of PMUs.
> 
> /sys/devices/system/node/node0/mem_ctlr0/
>                                         event_source_id
>                                         events/
>                                               partial_cacheline_read_retried/
>                                               partial_cacheline_write_retried/
>                                               ...
>                                mem_ctlr1/
>                                         event_source_id
>                                         events/
>                                               partial_cacheline_read_retried/
>                                               ...
> 
> So it's a bit ugly to replicate the event information across identical
> pmus, but that can be done via links, without too much memory cost, I
> assume.
> 
> Does this seem workable? 

If you really have two memory controllers per node, I guess so. Sounds
strange to me though, typically a memory controller is the node
boundary.

But like I said in the other email, use a 1:n pmu:event_source ratio and
simply stick then in the machine/device topology wherever they belong,
if that ends up with multiple PMUs at one particular level, so be it.