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How does the CPU know the GPU kernel is finished?

Question asked by dalibocai on Sep 24, 2014

I've been investigating how CPU knows when an OpenCL kernel running on GPU finishes. Are interrupts used? However, handling the interrupts can take even a longer time than the kernel runs. If the CPU uses polling, what's the frequency? I profiled the system calls and found that after each kernel invocation, there are exactly 5 yields. My guess is that those yields are used for the polling, but why only 5 times? Is it the case that after 5 polls, it switches to the interrupt mechanism?