@qwazctl commented in JENKINS-23012

I just noticed this ticket now, so sorry for the late comment. But taking a quick look at the code, the performance issue is quite obvious: in BuildTimeoutWrapper.decorateLogger you are only overriding write(byte) in the wrapper OutputStream - that is hugely inefficient, as most writes occur through write(byte[]) or write(byte[], int, int), and those translate to calling write(byte) one byte at a time. So, override write(byte[], int, int) too (write(byte[]) can be left as is) and I think you'll find a noticeable improvement.