Using a modprobe wrapper, I count 56 /sbin/modprobe calls taking ~4s (non-profiling udev) on my laptop, from which 23 are not found. 23 * /sbin/modprobe with a modalias, which is not found, sums up to ~1s (25%) of the time. So we can easily eliminate 25% of the modprobe time (on my laptop), by collecting all /sys/***/modalias at depmod time, which cannot be resolved, and store them in /lib/modules/$(uname -r)/modules.unresolved, which could be searched first by modprobe.