On Mar 20 2013, Valdis.Kletnieks@vt.edu wrote:
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.
Thanks for the correction. It appears I got wrong (outdated?) information from some book on kernel development, or perhaps simply misunderstood what I read. When I tried the example you gave, I saw the same thing, even on the older kernels I'm working with (2.6.32 in particular).
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.
-- Arlie (Arlie Stephens arlie@worldash.org)