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

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Date:	Mon, 5 Oct 2009 11:55:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, peterz@...radead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to
	get to performance counters


* Frederic Weisbecker <fweisbec@...il.com> 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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