Linux elevators (Re: BFQ: simple elevator)

[Valdis.Kletnieks at vt.edu]

On Wed, 20 Mar 2013 16:05:09 -0700, Arlie Stephens said:
> The ongoing thread reminds me of a simple question I've had since I
> first read about linux' mutiple I/O schedulers. Why is the choice of
> I/O scheduler global to the whole kernel, rather than per-device or
> similar?

They aren't global to the kernel.

On my laptop:

# find /sys/devices/pci* -name 'scheduler' | xargs grep .
/sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop deadline [cfq]
/sys/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/scheduler:noop deadline [cfq]
# echo noop >| /sys/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/schedule
# find /sys/devices/pci* -name 'scheduler' | xargs grep .
/sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop deadline [cfq]
/sys/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/scheduler:[noop] deadline cfq

I just changed the scheduler for the CD-ROM.


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