linux-kernel - Re: [PATCH v5 12/20] x86: perf: intel

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Date:	Tue, 11 Nov 2014 14:20:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, acme@...radead.org
Subject: Re: [PATCH v5 12/20] x86: perf: intel_pt: Intel PT PMU driver

On Tue, Nov 11, 2014 at 01:24:43PM +0200, Alexander Shishkin wrote:
> Peter Zijlstra <peterz@...radead.org> writes:

> > Now I'm not sure we want to export all the bits you're using though.
> > Like the topa_multiple_entires, that appears an implementation detail
> > userspace should not really care about either way.
> 
> Actually, userspace can make assumptions about lost data from this
> bit.

Do explain; it feels entirely wrong to expose something like this, esp.
since this crappy single TOPA thing is going away.

> But there are others, such as encoded address length. In future
> there will also be several "caps" with allowed values for certain bit
> fields in RTIT_CTL, such as timing packet frequencies.

No, those should not be caps, those should be in the format description.
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