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

Vince Weaver
2015-03-02T21:15:41Z

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