On Tue, Jun 23, 2009 at 8:54 PM, Kok, Auke<[email protected]> wrote: > Corrado Zoccolo wrote: >> Hi >> I have few suggestions for sreadahead, I hope this list is the proper >> place for them. >> >> * earlied versions of sreadahead used to put files under /etc, while >> version 1.0 uses /var. I find /etc to be more convenient, since I use >> a separate /var partition, and it is not yet mounted when >> rc.early.local is invoked (i.e. where I would like to start >> sreadahead) > > sreadahead uses /var to mount debugfs at the early stage, hence my choice to > move > this location to /var (I think /etc should be clear of mounts). > > I also think that the sreadahead pack file is not a configuration file, and as > such doesn't belong in /etc either. > > IMHO /var is the right location, if you want to have a specific /var > partition, > then I suggest that you delay starting up sreadahead until /var is mounted. >
Maybe having the prefix configurable may help. >> * use posix_fadvise(fd,off,len,POSIX_FADV_WILLNEED) instead of >> readahead(fs,off,len): posix_fadvise is non-blocking until there is >> room in the queue, so you can get rid of multithreading, and it will >> better interact with the block layer, allowing it to reorder more >> requests according to disk placement. > > I'm currently contemplating removing all the threading support, because I'm > not > seeing an improvement - even on SSD's. > Good. >> * export a plain file list of the files that are opened during boot. >> this list can be used by external script to optimize on-disk file >> placement for rotational disks. > > would a simple `dump` utility do? > Yes. >> * give an option to skip readahead of large contiguous blocks. This >> improves rotational disk performance when the disk is the bottleneck, >> since we prefetch all random accesses, that normally incur in high >> latency, and let the processes complete their sequential reads, that >> are faster, only when needed, with less contention. > > obviously for spinning discs only. I haven't really optimized sreadahead yet > for > this case, but this sounds like an ok idea. Have you tried it out? Yes. I'm using sreadahead 1.0 on 3 computers, 2 with rotational disks, and 1 ssd, and I found that on the rotational ones, prefetching only the small chunks (for me, small is <1M) helped to reduce the boot time. Corrado > > Auke > -- __________________________________________________________________________ dott. Corrado Zoccolo mailto:[email protected] PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- _______________________________________________ Power mailing list [email protected] http://www.bughost.org/mailman/listinfo/power
