On Tue, Jan 17, 2017 at 12:04 PM, Matthew Miller mattdm@fedoraproject.org wrote:
On Tue, Jan 17, 2017 at 04:38:31PM +0100, Jiri Eischmann wrote:
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.
It's my understanding that CFQ is better in the case where you a) have a single spinning disk with b) mixed workload on top of that and c) care about overall throughput more than latency. An example might be if you are a budget hosting provider and are running multiple VMs on single-disk servers. If is preferred for lower latency on desktops, and is overall preferred for servers (a win on RAID, on SSD, and even on single-disk systems in many cases), switching to as across-the-board default deadline seems like the straightforward choice.
I guess the next step is to engage the kernel team, and possibly FESCo since this is obviously a big engineering steering decision. And someone other than me can decide if this should be a Change.
That is a somewhat odd suggestion. It's a runtime tunable for a reason. No default will ever work for 100% of the cases Fedora may be used in. Rather than go through all the effort of making a decision for all of Fedora at the FESCo level, I would prefer the Workgroups look at what their target machine types are and come up with a default they would prefer to see. Then they can work on setting it at boot via an Edition specific setting.
josh