I found some problems with our (F8) readahead as it is. I did some testing w/ blktrace & seekwatcher during boot to see what the io patterns look like. First, the default/shipped readahead lists seem pretty incomplete, I saw lots of fresh IO happening after the readahead is done. How are the default lists maintained? I tried generating my own lists with init=/sbin/readahead-collector, but: Bugzilla Bug 326891: readahead-collector doesn't collect binaries I fixed that up, and generated nice long custom lists, but: Bugzilla Bug 327041: readahead --sort generates file with "(null)" instead of filename so after the cron.daily goes off, those nice custom lists (or the default lists) get nuked in the sort procedure. (I think this bug only hits on 32-bit platforms) Ok, fixed that up, and did a bit of other tweaking: 1) moved readahead_early to S01 per davej's suggestion, and made the readahead call *not* background itself. This seems to help. 2) also played with "readahead_later" at S02, reading ahead in the background. This saved a little time, but it requires jumping through hoops to make the lists properly. 3) tried adding a superearly readahead list for all the IO rc.sysinit does, it helped a little but not a whole lot. So, with the above bugfixes and 1) above, using (fixed) readahead *does* speed up the boot process. Testing w/o selinux so far, with stock readahead (0:59): http://sandeen.net/fedora_boot/bootchart-stockreadahead-noselinux.png http://sandeen.net/fedora_boot/seekwatcher-stockreadahead-noselinux.png without readahead (0:49): http://sandeen.net/fedora_boot/bootchart-noreadahead-noselinux.png http://sandeen.net/fedora_boot/seekwatcher-noreadahead-noselinux.png with tweaked readahead (0:44): (only tweak 1) above, with updated/sorted lists) http://sandeen.net/fedora_boot/bootchart-fixedreadahead-noselinux.png http://sandeen.net/fedora_boot/seekwatcher-fixedreadahead-noselinux.png On the seekwatcher graphs, nice linear accesses should be faster, and if all files are unfragmented and read-ahead in block order, we shouldn't be doing a lot of seeking around. I was able to get down to about 0:41 a few times with enough fiddling... Also, some way to keep the readahead lists uptodate would be a help, I think. Selinux still does have a lot of overhead, haven't started looking too closely at that case yet (for one, readahead probably doesn't pull in the selinux xattrs) Also, Chris Mason told me that the SuSE glibc has a patch which calls fadvise(POSIX_FADV_WILLNEED) on any shared library that is opened; this causes the kernel to launch its own readahead on it. I have the patch and will do some testing, sounds like an interesting approach. I'll keep looking at this... -Eric -- fedora-devel-list mailing list fedora-devel-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-devel-list
