On Tue, Apr 10 2012 at 3:55pm -0400, Jens Axboe <axboe@xxxxxxxxx> wrote: > On 2012-04-10 21:43, Mike Snitzer wrote: > > I'm still missing your position (other than you now wanting to make it > > a userspace concern). > > > > Put differently: why should CFQ still be the default? > > > > It is pretty widely held that deadline is the more sane default > > (multiple distros are now using it, deadline is default for guests, > > etc). CFQ has become more niche. The Linux default really should > > reflect this. > > > > The only case where defaulting to CFQ seems to make sense is > > rotational SATA (and USB). > > That's the precisely the reason it should still be the default. The > default settings should reflect a good user experience out of the box. > Most desktop machines are still using SATA drives. And even those that > made the leap to SSD, lots of those are still pretty sucky at high queue > depths or without read/write separation. So I'm quite sure the default > still makes a lot of sense. I agree that a default of CFQ still makes sense for SATA and USB. But why can't there be multiple defaults? default: deadline SATA and USB default: cfq > Punt tuning to the server side. If you absolutely want the best > performance out of your _particular_ workload, you are expecting and > required to tune things anyway. Not just the IO scheduler, but in > general. You can't make the same requirements for the desktop. Just because server admins are more used to tuning doesn't mean all server admins do it -- especially not on first evaluation. > As to kernel vs user, I just see little reason for doing it in the > kernel if we can put that policy in user space. There are distro packages that are shipped to control such knobs, e.g. tuned. They don't help _at all_ if the user doesn't know about them. Knob tuning is tedious on multiple levels. Much like this thread ;) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
