FOSDEM

I/O latency is the dominating factor in desktop application startup performance. It is also one of the hardest things to measure in a reliable and deterministic fashion. Wall-clock timings on just-booted, quiescent systems give unfeasibly large jitter making optimising cold-start times extremely difficult.

Measures of warm vs. cold start show eg. 80% of an OO.o cold start is pure I/O time. I/O grind is a new valgrind based tool that can record & simulate I/O patterns, allowing not only targeted optimisation of applications, but deterministic comparisons of kernel I/O algorithms. Kernel optimisation is often focused on more tractable CPU cycles, however the big wins are in I/O behavior - saving only one seek on cold OO.o startup, is the equivalent of a 500 cycle win on every system call emitted.