The cost of Linux's page fault handling
Linus wrote: 'Even a fully built kernel ("allmodconfig", so a pretty full build) takes about half a minute on my normal desktop to say "I'm done, that pull changed nothing I could compile".'Since it's just after a git operation all the file state should be warm in the disk cache.  It really shouldn't take that long.  The Linux kernel (at least by looking at [1]) is about the same size in terms of file count as Chromium, and we got this operation down to about a second by using better tools (i.e. non-recursive make and then eventually a replacement).I appreciate that the kernel has its own requirements (it sounds like his no-op builds are still running shell scripts, something you ought to avoid in your critical path) and also it's great that he's running it this way in part to help profile a "normal" workload... but I'm also a bit sad to see so much time spent waiting for something slower than necessary, as well as time spent optimizing what feels like the wrong thing.[1]: http://larjona.wordpress.com/2011/06/15/numbers-about-the-li...