[Intel-gfx] [RFC 1/8] drm/i915: Have globally unique context ids, as opposed to drm file specific

[Chris Wilson]

On Wed, Jul 15, 2015 at 02:16:56PM +0530, sourab.gupta at intel.com wrote:
> From: Sourab Gupta <sourab.gupta at intel.com>
> 
> Currently the context ids are specific to a drm file instance, as opposed
> to being globally unique. There are some usecases, which may require
> globally unique context ids. For e.g. a system level GPU profiler tool may
> lean upon the context ids to associate the performance snapshots with
> individual contexts. If the context ids are unique, it may do so without
> relying on any additional information such as pid and drm fd.
> 
> This patch proposes an implementation of globally unique context ids, by
> conceptually moving the idr table for holding the context ids, into device
> private structure instead of file private structure. The case of default
> context id for drm file (which is given by id=0) is handled by storing the
> same in file private during context creation, and retrieving as and when
> required.
> 
> This patch is proposed an an enabler for the patches following in the
> series. In particular, I'm looking for feedback on the pros and cons of
> having a globally unique context id, and any specific inputs on this
> particular implementation. This implementation can be improved upon, if
> agreed upon conceptually.

Simpler: use a cyclic idr for global context ids. The importance here is
that for the common case we have a more friendly per-file small lookup
table and reporting, also the code should be more understandable with a
separate user_handle and guid.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre