Quoting Lionel Landwerlin (2018-02-12 10:37:52)
> On 09/02/18 20:53, Chris Wilson wrote:
> > Quoting Lionel Landwerlin (2018-02-09 17:47:44)
> >> Hey Chris,
> >>
> >>   From the i915/perf point of view, I'm fine with this change.
> >> The pinning of the hw_id when monitoring a single context (with OA)
> >> doesn't break the existing userspace (I can only think of Mesa).
> >>
> >> I'm also trying to build up a system wide monitoring feature in GPUTop
> >> with a timeline display. This change makes it a bit more challenging.
> >> But this isn't really an expected feature, it's just nice to have.
> >>
> >> What I'm thinking of would be to keep a circular buffer of requests in
> >> the order they're submitted to an engine.
> >> Then the i915 perf driver could correlate between the context-switch
> >> tagged reports coming from OA and the requests submitted.
> >> Much like the OA buffer, this circular buffer could overflow at which
> >> point we signal the application using the i915 perf driver and it'll
> >> most likely close the driver and try again.
> >>
> >> I would need that have the hw_id added to the requests. Does that sounds
> >> possible?
> > You already add hw_id to the tracepoint. For the requests, it is just
> > req->ctx->hw_id, valid from submission to retirement. Hmm, the
> > tracepoint is broken (use-after-free in ctx->hw_id). What value do you
> > want for HSW? (This patch will assign all legacy submission to HW ID 0.)
> > But aiui, for HSW oa you want lrca not HW ID. So both the use-after-free
> > and alternative ids suggest storing it on the request directly.
> HSW doesn't have a hw_id field in the OA reports.
> I'll have to come up with something slightly different.
> >
> > How do you get the HW ID out, via the tracepoint right?
> It's in the OA reports.

I mean how do you correlate the HW ID with userspace?
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