Can't the two schedulers coexist in some way? I'm ignorant about that, but it obviously would be the better solution, because penalizing HDD users (which are more than SSD users, not only in the desktop market) sounds like a bad idea.
I wonder if IO-scheduler should be a mount option.
No, because it is not a feature at the file-system level, also I would imagine the kernel only creates a per-disk queue, rather than a per-partition queue. If it were a mount option, you could get conflicts about what block on the device the kernel should access next. (It would require you write a scheduler to schedule each schedulers access to the block device, which is messy to say the least)
Originally Posted by mrugiero
Is the IO scheduler defined on build time or mount time (or any other criteria I can't think about)? How do I change it if it's not defined at build time?
There is a sysFS interface for per-disk schedulers.