On Tue, May 11, 2021 at 04:49:58PM +0200, Daniel Vetter wrote: > 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? > Yep, noticed this after sending. > > * 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 :-) > Sounds like a fun conversation, will do. > > + > > +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. > Sure. This is a limitation of the GuC interface + really isn't needed unless we have more than 2 engines of the same type. > > + > > +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. > Yes, we can limit the submit to N batchbuffers. In fact I want too. I think 1-N is a layover from our internal discussions where we wanted this interface to be able to do everything and anything. > 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? > I think we just drop this per the comments above. If we only allow N batch buffers on a contexts configured with 'set_parallel' we really don't need to pass in the number of buffers do we? Matt > Cheers, Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch
