3 ms·

> At one point, a disk read was CPU-bound. That sounds impressive. Could you say more about how/why?

• mcguire 7y ago
  1. Keep in mind that the programmers had swallowed gallons of the multi-server microkernel koolaid, so the flow was user code -> mk -> file server -> mk -> device driver and back. 2. Someone used the wrong magic keywords in the mig spec, causing poor message send-receive structure and code. 3. The same someone, IIRC, set up the copy on write memory management for each page, rather than one big buffer. The latter would still be slower than just copying, but geeze. 4. There was something wrong with the driver at the time; I never heard what. 5. In fairness, there was some overhead from our monitoring.