[Intel-gfx] [PATCH 03/15] drm/i915: Framework for capturing command stream based OA reports

[Martin Peres]

On 02/06/16 08:18, sourab.gupta at intel.com wrote:
> From: Sourab Gupta <sourab.gupta at intel.com>
>
> This patch introduces a framework to enable OA counter reports associated
> with Render command stream. We can then associate the reports captured
> through this mechanism with their corresponding context id's. This can be
> further extended to associate any other metadata information with the
> corresponding samples (since the association with Render command stream
> gives us the ability to capture these information while inserting the
> corresponding capture commands into the command stream).
>
> The OA reports generated in this way are associated with a corresponding
> workload, and thus can be used the delimit the workload (i.e. sample the
> counters at the workload boundaries), within an ongoing stream of periodic
> counter snapshots.
>
> There may be usecases wherein we need more than periodic OA capture mode
> which is supported currently. This mode is primarily used for two usecases:
>     - Ability to capture system wide metrics, alongwith the ability to map
>       the reports back to individual contexts (particularly for HSW).
>     - Ability to inject tags for work, into the reports. This provides
>       visibility into the multiple stages of work within single context.
>
> The userspace will be able to distinguish between the periodic and CS based
> OA reports by the virtue of source_info sample field.
>
> The command MI_REPORT_PERF_COUNT can be used to capture snapshots of OA
> counters, and is inserted at BB boundaries.

So, it is possible to trigger a read of a set of counters (all?) from 
the pushbuffer buffer?

If so, I like this because I was wondering how would this work break 
when we move to the GuC-submission model.

Thanks for working on this!
Martin