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 11:24:53 +0200
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to get 
	to performance counters

2009/10/5 Ingo Molnar <mingo@...e.hu>:
>
> * Peter Zijlstra <peterz@...radead.org> wrote:
>> Non-trivial.
>>
>> Something like this would imply a single output channel for all these
>> CPUs, and we've already seen that stuffing too many CPUs down one such
>> channel (using -M) leads to significant performance issues.
>
> We could add internal per cpu buffering before it hits any globally
> visible output channel. (That has come up when i talked to Frederic
> about the function tracer.) We could even have page sized output (via
> the introduction of a NOP event that fills up to the next page edge).


That looks good for the counting/sampling fast path, but would that scale
once it comes to reordering in the globally visible output channel?
Such a union has its costs.
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