Linux elevators (Re: BFQ: simple elevator)

[Arlie Stephens]

On Mar 20 2013, Valdis.Kletnieks at 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 It appears I got wrong (outdated?)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 at worldash.org)