On Thu, May 06, 2021 at 10:30:46AM -0700, Matthew Brost wrote: > Add entry fpr i915 new parallel submission uAPI plan. > > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > Cc: Tony Ye <tony.ye@xxxxxxxxx> > CC: Carl Zhang <carl.zhang@xxxxxxxxx> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx> > Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > --- > Documentation/gpu/rfc/i915_scheduler.rst | 56 +++++++++++++++++++++++- > 1 file changed, 54 insertions(+), 2 deletions(-) > > diff --git a/Documentation/gpu/rfc/i915_scheduler.rst b/Documentation/gpu/rfc/i915_scheduler.rst > index fa6780a11c86..e3455b33edfe 100644 > --- a/Documentation/gpu/rfc/i915_scheduler.rst > +++ b/Documentation/gpu/rfc/i915_scheduler.rst > @@ -13,7 +13,8 @@ i915 with the DRM scheduler is: > modparam enable_guc > * Lots of rework will need to be done to integrate with DRM scheduler so > no need to nit pick everything in the code, it just should be > - functional and not regress execlists > + functional, no major coding style / layering errors, and not regress > + execlists I guess this hunk should be in the previous patch? > * Update IGTs / selftests as needed to work with GuC submission > * Enable CI on supported platforms for a baseline > * Rework / get CI heathly for GuC submission in place as needed > @@ -67,4 +68,55 @@ levels too. > > New parallel submission uAPI > ============================ > -Details to come in a following patch. > +The existing bonding uAPI is completely broken with GuC submission because > +whether a submission is a single context submit or parallel submit isn't known > +until execbuf time activated via the I915_SUBMIT_FENCE. To submit multiple > +contexts in parallel with the GuC the context must be explictly registered with > +N contexts and all N contexts must be submitted in a single command to the GuC. > +This interfaces doesn't support dynamically changing between N contexts as the > +bonding uAPI does. Hence the need for a new parallel submission interface. Also > +the legacy bonding uAPI is quite confusing and not intuitive at all. I think you should sit together with Jason on irc or so for a bit and get an earful of how it's all broken irrespective of GuC submission or not. Just to hammer in our case :-) > + > +The new parallel submission uAPI consists of 3 parts: > + > +* Export engines logical mapping > +* A 'set_parallel' extension to configure contexts for parallel > + submission > +* Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > + > +Export engines logical mapping > +------------------------------ > +Certain use cases require BBs to be placed on engine instances in logical order > +(e.g. split-frame on gen11+). The logical mapping of engine instances can change > +based on fusing. Rather than making UMDs be aware of fusing, simply expose the > +logical mapping with the existing query engine info IOCTL. Also the GuC > +submission interface currently only supports submitting multiple contexts to > +engines in logical order. Maybe highlight more that this is a new restriction with GuC compared to execlist, which is why we need to expose this information to userspace. Also on the platforms thus far supported in upstream there's at most 2 engines of the same type, so really not an issue. > + > +A single bit will be added to drm_i915_engine_info.flags indicating that the > +logical instance has been returned and a new field, > +drm_i915_engine_info.logical_instance, returns the logical instance. > + > +A 'set_parallel' extension to configure contexts for parallel submission > +------------------------------------------------------------------------ > +The 'set_parallel' extension configures N contexts for parallel submission. It > +is setup step that should be called before using any of the contexts. See > +I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE or I915_CONTEXT_ENGINES_EXT_BOND for > +similar existing examples. Once the N contexts are configured for parallel > +submission the execbuf2 IOCTL can be called submiting 1-N BBs in a single IOCTL. > +Although submitting less than N BBs is allowed it is not recommended as that > +will likely leave parts of the hardware reserved and idle. Initially only > +support GuC submission. Execlist support can be added later if needed. Can we just require that you always submit N batchbuffers, or does this create a problem for userspace? Allowing things just because is generally not a good idea with uapi, it's better to limit and then allow when there's a need. Ofc if we already have a need then explain why and that's all fine. Also detailed comments on the kerneldoc I'll do in the next patches. > + > +Add I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT and > +i915_context_engines_parallel_submit to the uAPI to implement this extension. > + > +Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > +------------------------------------------------------------------- > +Contexts that have been configured with the 'set_parallel' extension are allowed > +to submit 1-N BBs in a single execbuf2 IOCTL. The BBs are either the last N > +objects in the drm_i915_gem_exec_object2 list or the first N if > +I915_EXEC_BATCH_FIRST is set. > + > +Add field 6 bit wide field to drm_i915_gem_exec_object2.flags which indicates > +the number of BBs - 1 included in the IOCTL. Hm we have the nice execbuf extension chaining, any reason for not using that and instead opting for clever field packing? Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
