Slow PA capture on Vulkan apps

Streamline fails to capture data from a Vulkan application when using the lwi_me.py script with --lwi-mode set to capture. Streamline connects to the device and the capture starts, but the frame rate drops to below 10FPS, and the application on the device runs very slowly, not in real-time as would be expected.

Condition

Vulkan applications, Arm Mobile Studio version 2020.3 and earlier.

Cause

Arm Mobile Studio's lightweight interceptor (LWI) can only capture frames from your application if the interceptor API layer and midstream are active. This causes a problem when capturing data from Vulkan applications. We are working on a fix to this issue, to be included in a future release.

Workaround

If you are not interested in capturing slow frames, run lwi_me.py with --lwi-mode set to none. This will enable you to generate a capture, but will not show slow frame images on the frame analysis chart in Performance Advisor. 

If you need to capture slow frames, a workaround is to capture the frame numbers first in 'tag' mode and then capture those frames in 'replay' mode as described in Tagging slow frames in the Performance Advisor user guide.

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