Re: [patch 2/3] performance counters: documentation

From: David Miller
Date: Thu Dec 04 2008 - 22:27:06 EST

From: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Date: Thu, 4 Dec 2008 18:50:02 -0800

> I would like to respectfully disagree with this some. The kernel needs
> to abstract hardware to some degree for userspace. The problem in this
> case is that userspace can't really do a better job, in fact it can
> only do a worse job since it lacks the coordination capability of
> knowing it has full control of all the hardware registers.

The perfmon context abstraction dealt with that. Code using the
perfmon interfaces provided a set of counter and control register
values to the kernel.

The kernel merely loaded and unloaded them when a process (or group of
processes) ran.

The kernel is a validity checker, and that minimal stuff is exactly
what the perfmon kernel component implemented.
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