Linux elevators (Re: BFQ: simple elevator)
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? Consider a system with both traditional rotating disks and SSDs - not at all far fetched. An appropriate I/O scheduling algorithm for rotating disks is likely to do a lot of work that's useless for SSDs. Why require that the same algorithms be used for both? -- Arlie (Arlie Stephens ar...@worldash.org) ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Linux elevators (Re: BFQ: simple elevator)
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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop deadline [cfq] /sys/devices/pci:00/:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/scheduler:noop deadline [cfq] # echo noop >| /sys/devices/pci:00/: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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop deadline [cfq] /sys/devices/pci:00/: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. pgp0_KZpObd65.pgp Description: PGP signature ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Linux elevators (Re: BFQ: simple elevator)
On Mar 20 2013, valdis.kletni...@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 It appears I got wrong (outdated?)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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop > deadline [cfq] > /sys/devices/pci:00/:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/scheduler:noop > deadline [cfq] > # echo noop >| > /sys/devices/pci:00/: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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop > deadline [cfq] > /sys/devices/pci:00/: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 ar...@worldash.org) ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Linux elevators (Re: BFQ: simple elevator)
On Wed, Mar 20, 2013 at 4:45 PM, Arlie Stephens wrote: > On Mar 20 2013, valdis.kletni...@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. Yeah, the "global" thing is just the system default. It's what newly created or discovered block devices will be assigned initially. > 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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop >> deadline [cfq] >> /sys/devices/pci:00/:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sr0/queue/scheduler:noop >> deadline [cfq] >> # echo noop >| >> /sys/devices/pci:00/: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/pci:00/:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler:noop >> deadline [cfq] >> /sys/devices/pci:00/: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 ar...@worldash.org) > > ___ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
