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»I/O Trace - Michael Meeks
Biography
Michael is a Christian and enthusiastic believer in Free software. He very much enjoys working for Novell where as a member of the Desktop research team he has worked on desktop infrastructure and applications, particularly OpenOffice.org, CORBA, Bonobo, Nautilus and accessibility, amongst other interesting things. He now works as an Architect, trying to understand and nudge the direction of our Linux Desktop work. Prior to this he worked for Quantel gaining expertise in real time AV editing and playback achieved with high performance focused hardware / software solutions.
Abstract
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.
