198684 2019-06-07 15:55:28 -0700 [WebGPU] Performance: Cache staging MTLBuffers used by GPUBuffer.unmap 2019-06-07 16:00:45 -0700 1 1 1 Unclassified WebKit WebGPU WebKit Nightly Build Unspecified Unspecified NEW InRadar P2 Normal --- 1 justin_fan webkit-unassigned webkit-bug-importer oldest_to_newest 1542988 0 justin_fan 2019-06-07 15:55:28 -0700 GPUBuffers created with GPUDevice.createBufferMapped are not CPU-accessible if they are not created with MAP_WRITE or MAP_READ usage. This necessitates a copy of written data to a CPU/GPU shared MTLBuffer, before copying this staging buffer to the intended destination on the GPU, during the call to GPUBuffer.unmap. Since MTLBuffer creation is expensive, we can cache reasonably-sized (TBD size) staging buffers for re-use on the GPUDevice. A GPUBuffer can re-use the device's staging buffer for its unmap call, or create a new one if one does not exist or is too small. If the staging buffer is not used within a certain time (TBD, i.e. ~10 frames), it is released. Bonus points: implement a (sorted?) LRU-cache of different-sized staging buffers and use the smallest one that will suffice. This would release unusually large staging buffers earlier, but require more storage overall. 1542990 1 webkit-bug-importer 2019-06-07 15:58:48 -0700 <rdar://problem/51539224> 1542991 2 webkit-bug-importer 2019-06-07 15:58:48 -0700 <rdar://problem/51539225> 1542993 3 justin_fan 2019-06-07 16:00:33 -0700 Small addition: Specify MTLResourceCPUCacheModeWriteCombined in the creation option for these staging buffers, as the CPU never reads from them.