So on the recent config DMABuf is less effective than the former one. From detailed CPU usage with Dmabuf Firefox uses 50-60% cpu and without it it uses 30-40%. The BMABuf may have one advantage that compositor may handle us raw GPU buffer and we can drop them if nobody needs them without any processing (Bug 1820971). From my testing that may reduces screensharing CPU usage by 50%.
Bug 1819035 Comment 75 Edit History
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So on the recent config DMABuf is less effective than the former one. Note that the pictures measure CPU usage of whole system, i.e compositor + Firefox. From detailed CPU usage with Dmabuf Firefox uses 50-60% cpu and without it it uses 30-40%. The BMABuf may have one advantage that compositor may handle us raw GPU buffer and we can drop them if nobody needs them without any processing (Bug 1820971). From my testing that may reduces screensharing CPU usage by 50%.