Re: [RFC PATCH] perf_core: provide a kernel-internal interface toget to performance counters

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:

> Can't we instead modify the perf events to be able to run on multiple 
> contexts?
> 
> We could change struct perf_event::ctx into a list of context and then 
> attach it to several cpu contexts.
> 
> The perf event struct have been designed to run on only one context so 
> its structure and handling does not deal with races due to concurrent 
> uses I guess. But at a first glance, few things would need to be 
> modified to handle that, and at a low cost.
> 
> There might be bad corner cases I forget though...

Dunno, i assumed it wouldnt be possible sanely. If you tried a patch we 
could argue about the particulars ...

This would in essence create a new event type: system-wide. It doesnt 
scale in its naive implementation - which would be fine for low freq 
events.

We could encode it via sys_perf_event_open(pid:-1, cpu:-1).

	Ingo
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