Re: [PATCH 0/9] drm/syncobj: Add full-featured wait support (v2)

Christian König <christian.koenig@xxxxxxx> · Tue, 22 Aug 2017 10:30:53 +0200



    Am 21.08.2017 um 23:42 schrieb Jason
      Ekstrand:

    
          On Wed, Aug 16, 2017 at 1:10 PM,
            Jason Ekstrand <jason@xxxxxxxxxxxxxx>
            wrote:

            
                    On Wed, Aug 16, 2017 at
                      9:53 AM, Christian König <christian.koenig@xxxxxxx>
                      wrote:

                      
                            [SNIP]

                                
                                              See a wait_queue is a
                                              callback mechanism anyway,
                                              so you are wrapping a
                                              callback mechanism inside
                                              another callback mechanism
                                              and that makes not really
                                              much sense.

                                            
                                        Fair enough.  There is one
                                          little snag though:  We need
                                          to wait on sync objects and
                                          fences at the same time in
                                          order for WAIT_ANY |
                                          WAIT_FOR_SUBMIT to work.  I
                                          see two options here:

                                          
                                         1) Convert dma-fence to
                                          use waitqueue instead of its
                                          callback mechanism and add a
                                          wait_queue_any.  A quick grep
                                          for dma_fence_add_callback
                                          says that this would affect
                                          four drivers.

                                        
                                The more I think about it, the less
                                sense using waitqueues makes.  The
                                fundamental problem here is that the
                                event we are waiting on is actually the
                                concatenation of two events: submit and
                                signal.  Since we are waiting on several
                                of these pairs of concatenated events
                                simultaneously, the only two options we
                                have are to either combine them into one
                                event (the proxy approach) or to
                                implement a wait which is capable of
                                handling both at the same time.  I don't
                                see a way to do the latter with wait
                                queues.

                              
                            Agree completely.

                              
                              Essentially we would need to enable
                              wait_event_* to wait for multiple events
                              and then convert all the fence callback
                              stuff to wait_event structures.

                              
                              But that is certainly outside the scope of
                              this patchset, so feel free to go ahead
                              with the approach of waiting manually (but
                              please without the bugs).

                            
                Well, the patches I sent last
                  night should do just that.  It's mostly the original
                  approach but with the bugfixes from versions 3 and 4. 
                  Modulo finding additional bugs, I think they should be
                  good to go.
              
            
        ping?

        
    I just way to much to do at the moment (as usually). Feel free to
    add an Acked-by: Christian König <christian.koenig@xxxxxxx> to
    the patches in the meantime, but an detailed review would have to
    wait a bit.

    
    Sorry for the delay,

    Christian.

  
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