Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS_INTR support

[Vince Weaver]

On Mon, 2 Mar 2015, Stephane Eranian wrote:

> vince,

> PEBS machine state. Problem is that there is only one set of pt_regs passed to
> __intel_pmu_pebs_event(). And if REGS_INTR is set, then the pt_regs
> registers are
> indeed overwritten with PEBS captured state. To avoid the issue, we
> would have to
> carry around two sets of pt_regs.

I don't think we have to carry around both (would that ever be useful?)
Just that the behavior is a bit surprising and I should document it in the 
manpage.

One question I do have: if it never makes sense to measure REGS_USER and 
REGS_INTR at the same time, why was the latter added at all?  Why not just 
have the REGS_USER information automatically upgrade to REGS_INTR if 
precise_ip is high enough?

Vince

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