[SOLVED] Old-fashioned HDDs and multi-queue block layer / lack of I/O scheduler

the dsc · 02-14-2015, 12:44 AM

I know less about it than it may sound... pretty much clueless, really.

If you don't have an SSD, would you be better off with the old "equivalent" of blk-mq, or however you'd properly phrase the previous state, with I/O schedulers instead? (Lacking as of kernel 3.17, and I think 3.18 too -- thread on Gentoo forums about this issue)

I ask because if I cat /sys/block/sda/queue/scheduler

The output is "none". The same for any "sd".

Is the previous state something that requires compiling a new kernel, or can it usually be set by grub parameters?

Answering myself on the last question, at least, it seems that "yes":

Quote:

Note:
Kernel defaults to using BFS CPU scheduler and CFQ IO scheduler.
Add elevator=bfq in kernel command line to use BFQ IO scheduler instead without recompiling.

https://pateo.wordpress.com/2014/08/...ng-2014-07-19/

Valid at least for liquorix 3.15 -- seems to not work anymore for the most recent one, 3.18. The grub line gave me "none" when I run "cat", and even echoing wouldn't change anything. With the stock Debian kernel it's normal, showing the scheduler set at boot time.

Keruskerfuerst · 02-14-2015, 10:08 AM

Yes, you can compile multiple i/o schedulers into the kernel and select them by passing a boot parameter to the kernel.