timing consecutive events in cuda

Question

If you have multiple consecutive CUDA events (in a single stream) that you'd like to time (e.g. cudaMemcpy followed by a kernel launch followed by another cudaMemcpy), is it safe/proper/accurate to synchronize only on the last event? For example:

cudaEventRecord(event1_start);
// do something
cudaEventRecord(event1_stop);

cudaEventRecord(event2_start);
// do something else
cudaEventRecord(event2_stop);

cudaEventSynchronize(event2_stop);
cudaEventElapsedTime(&time1, event1_start, event1_stop);
cudaEventElapsedTime(&time2, event2_start, event2_stop);

My understanding is that these events and actual cuda calls get placed into a FIFO queue. The CPU then needs to only wait until the last event is recorded before it records timings for all. Is this correct?

Thanks!

jmsu jmsu · Accepted Answer · 2011-06-28T08:15:13

If they are all executed in the same stream or the default stream they will be executed sequentially so I'd say yes, if you synchronize only the last one the others should be finished. I don't guarantee it because I never tested it. I suggest you test it with a simple case where you synchronize both events or only the last one and then compare the times.

timing consecutive events in cuda

1 Answers