linux-kernel - Re: re-enable Nehalem raw Offcore-Events support

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Message-ID: <alpine.DEB.2.00.1104301659230.8618@cl320.eecs.utk.edu>
Date:	Sat, 30 Apr 2011 17:03:51 -0400 (EDT)
From:	Vince Weaver <vweaver1@...s.utk.edu>
To:	Borislav Petkov <bp@...en8.de>
cc:	Ingo Molnar <mingo@...e.hu>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...il.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>
Subject: Re: re-enable Nehalem raw Offcore-Events support

On Sat, 30 Apr 2011, Borislav Petkov wrote:
> On Fri, Apr 29, 2011 at 10:17:04PM -0400, Vince Weaver wrote:

> > Well guess what, AMD family 15h changes all of that.
> 
> I don't see a big problem here, Robert has a patch that takes care of
> counter constraints. It probably needs a bit more work but we'll get
> where we need to be.

yes, but it's a bit of a change from the PMU of previous AMD chips,
going against Ingo's argument that the featureset of all modern CPUs is 
somehow converging.

> > And you're not going to like LWP. They got tired of waiting for a
> > workable kernel perf counter interface and moved it completely to
> > usersapce,
> 
> I don't know where you get your information but that's absolutely and
> completely not nearly even beginning to smell the truth.

I talked with someone fairly involved in the development with LWP who 
implied as much in an off-the-record discussion.  You have to admit back
5-6 years old when LWP was being planned it wasn't certain that kernel 
support for perf events was *ever* going to make it into Linux.
Though maybe AMD is more concerned about the even worse support in other 
OSes.  It's true you'd probably know better.

> Look at tip/x86/xsave, looks like LWP support will most likely be in
> 2.6.40.

Really?  Does Ingo know yet?  I get the impression he doesn't like 
perf-event features slipping in under the radar like that.

Vince

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