[PATCH] D75531: [mlir][vulkan-runner] Add basic timing for compute pipeline

[Ben Vanik via Phabricator via llvm-commits]

benvanik added inline comments.


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Comment at: mlir/tools/mlir-vulkan-runner/VulkanRuntime.cpp:722
+    // Get anotehr timestamp after invoking the compute shader.
+    vkCmdWriteTimestamp(commandBuffer, VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
+                        queryPool, 1);
----------------
antiagainst wrote:
> benvanik wrote:
> > you want to insert this after the vkCmdDispatch below - the timestamp only latches the value after previous commands complete (in this case, just the timestamp reset/initial query)
> Thanks! I find the spec a bit difficult to parse: "latches the value of the timer when all previous commands have completed executing as far as the specified pipeline stage". I interpret it as the pipeline stage (`VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT`) controls when to write out the timestamp, not the placement of the `vkCmdWriteTimestamp` command. (Otherwise the pipeline stage specification does not really make sense.) But I do see there is a difference if I move the second `vkCmdWriteTimestamp` below `vkCmdDispatch`. So I'm a bit puzzled here.
I believe that vkCmdWriteTimestamp acts as an implicit vkCmdPipelineBarrier with the srcStageMask set to what you pass in (BOTTOM_OF_PIPE), so it effectively partitions the command buffer into two synchronization scopes based on the order the commands were recorded.


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https://reviews.llvm.org/D75531