What I’ve discovered is that when you tax the CPU more than a few seconds, you get throttled back almost to a standstill. I put together a brief video where I demonstrate this happening. In this video, I run a simple script that makes repeated calls to sysbench to tax the CPU for 2 seconds. After it runs for a few times, you’ll see an immediate and severe reduction in performance and you’ll see the steal time go to over 97% leaving very little left to run my job.
» I have been using my Micro Instance lately to do some batch image processing. After having it run most of the night, I discovered that the problem is due to this steal time and the burst nature of the EC2 micro instance. Looks like it’s time to temporarily upgrade to a High-CPU instance :).