Re: amdgpu doesn't do implicit sync, requires drivers to do it in IBs

Christian König <ckoenig.leichtzumerken@xxxxxxxxx> · Thu, 28 May 2020 11:11:31 +0200



    Well we still need implicit sync or
      otherwise the GPU scheduler would pick up the jobs in the wrong
      order.

      
      See without this when we have the following sequence of
      submission:

      
      Client IB1 using buffer A

      Client IB2

      X IB1 using buffer A

      
      We could end up with the execution order

      
      X IB1 using buffer A

      Client IB1 using buffer A

      Client IB2

      
      And that is not correct. The scheduler is only allowed to do the
      following:

      
      Client IB1 using buffer A

      X IB1 using buffer A

      Client IB2

      
      And that's what implicit sync is taking care of.

      
      Christian.

      
      Am 26.05.20 um 00:07 schrieb Marek Olšák:

    
        If a user mode driver is changed to rely on the existence
          of implicit sync, it results in corruption and flickering as
          reported here: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2950
        

        Marek

        
        On Mon, May 25, 2020 at 6:05
          PM Marek Olšák <maraeo@xxxxxxxxx> wrote:

        
            Hi Christian,
            

            Bas and Michel wanted to discuss this. The main
              disadvantage of no implicit (pipeline) sync within the
              same queue is that we get lower performance and lower GPU
              utilization in some cases.

            
            We actually never really needed the kernel to have
              implicit sync, because all user mode drivers contained
              hacks to work without it.
            

            Marek

            
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