On Sat, Oct 11 2008, Arjan van de Ven wrote: > On Sat, 11 Oct 2008 18:38:44 +0200 > James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > On Sat, 2008-10-11 at 09:04 -0700, Arjan van de Ven wrote: > > > On Sat, 11 Oct 2008 17:44:13 +0200 > > > James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > So we need something a bit more involved, but not too complex. A > > > > > fine line... > > > > > > > > It's a policy ... just let userspace do it so the user can tune > > > > it. That's what EMC does now (except I think they key of inquiry > > > > strings rather than cache size). > > > > > > > > > while the chosen elevator obviously is policy, the kernel really > > > should pick a sensible default based on what it knows. > > > Lets put it this way: if userland needs to do a tuning to the kernel > > > based on data only provided by the kernel, and will always do it the > > > same way, we should have made that choice the default policy in the > > > kernel in the first place. > > > > Well, this is a bit of a nasty layering problem. We certainly don't > > want the Block layer to know how to poke at SATA, SCSI and other > > esoteric media to see what elevator should be the default, so we'd > > have to craft a new block API that the lower subsystems would > > implement for this. I'm really not sure it's worth the trouble when > > the boot system can do it simply from userspace, but I'll defer to > > Jens. > > > > these devices already give the elevator layer information about the > device, like optimal/max io size etc. > having the elevator take a "don't bother optimizing for seeks" flag > is very much along the same lines, it's a device property that the > elevator needs to learn about in order to send the right kinds of IO > down. Completely agree. And this is very different from the 'choose elevator based on device properties', a way of thinking that I don't agree with. This 'non rotational' flag does just that, passes down more information to the IO scheduler so it can make more informed choices. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
