The post is about chasing the long tail of latency risk. A high -- even very high -- probability of not acquiring a lock is not good enough. Investigating libmalloc and discovering that somehow it had strictly bounded, suitable execution time wouldn't be good enough either, because it could plausibly change without notice.
Suppose a deadline of 6ms to produce an audio buffer. If 0.01% of the callbacks choke on a lock, we get a dropout once a minute, which is quite a lot. This means we're interested in the 99.99th percentile.
