Matthew Miller píše v Po 16. 01. 2017 v 20:19 -0500:
On Mon, Jan 16, 2017 at 06:07:42PM -0600, Michael Catanzaro wrote:
http://www.hecticgeek.com/2016/12/fedora-25-review/ It includes a couple recommendations: * We should restore systemd-readahead to speed boot time by ~30% for users without SSDs. Endless has a downstream patch for this. Or we could use Ubuntu's readahead utility.
Has Endless done benchmarks? I'd hate to renable it based mainly on anecdotes. If it turns out to be worthwhile, it'd be nice to work with Endless to get the feature back upstream in systemd - if I remember right, one of the points at its removal was that the main developers didn't have the spinning-disk hardware to benefit from it and that no one who cared stepped up. If it turns out that there _are_ people who care, upstream seems like the right home.
* We should switch from CFQ to deadline I/O scheduler (which Ubuntu has been using for years) for subjective massive responsiveness improvements when the system is under load
Same point about benchmarks applies here, although it's a lot less work to experiment with and the consequences easily reversed. FWIW, RHEL 7 defaults to deadline on all devices except SATA disks, which default to CFQ. And on virtual disks, you get no IO scheduling at all, which makes sense and makes this irrelevant in those cases
I briefly spoke with Jiri Hladky, the manager of the FS perf team in Red Hat, and he says that deadline is clearly better for SSD. Results for rotating disks are mixed, but he'd still prefer deadline there, too. He can provide more detailed info if we need it.
Jiri