linux-kernel - Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units

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Message-ID: <20131219150226.GH16438@laptop.programming.kicks-ass.net>
Date:	Thu, 19 Dec 2013 16:02:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow
 tracing units

On Thu, Dec 19, 2013 at 03:49:42PM +0100, Frederic Weisbecker wrote:
> On Thu, Dec 19, 2013 at 04:30:53PM +0200, Alexander Shishkin wrote:
> > Or the interface and implementation of BTS support in the kernel
> > discourage its use and that is why it is so rarely used.
> 
> I never heard complains about it. It's a simple dump of from/to address couples.
> I just think nobody take the time to develop userspace tooling to exploit it.
> But it's famous slowness might have had a bad influence on this. And may be
> also the fact that it's very architecture specific. AMD doesn't support BTS if I recall
> correctly. Or may be it has its own different implementation?

No AMD doesn't do anything like that.

There was some attempt to cure some of the wobblies:

  https://lkml.org/lkml/2013/7/8/154

But people never pursued that.

That said, if people want overwrite mode to work for PT we'd need to fix
the same thing.
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