Re: [PATCH v5 12/20] x86: perf: intel_pt: Intel PT PMU driver

[Peter Zijlstra]

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