Messages in this thread |  | | | Date | Mon, 22 Mar 1999 22:05:12 -0500 | | From | Mark Lord <> | | Subject | Re: disk head scheduling |
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Linus Torvalds wrote: .. > This of it as "scheduling entity". It then depends a lot on the actual > hardware what such a scheduling entity is. > > For example, for floppy drives and IDE disks, you really cannot schedule > across the controller, because while there are multiple devices per > controller, they are not independent of each other.
Actually, sometimes we can (and do) schedule multiple devices for overlapped I/O on the same controller. ATAPI devices (cdrom, tape, zip/floppy) can overlap some operations with a hard disk (or other ATAPI) on the same cable/controller.
And I think Gadi added per-device (rather than per-controller) queues somewhere in the 2.1.xx timeframe, to improve performance of disk<->tape backups on a single controller.
ATA4/ATA5 now include "queued commands" for even more overlap, pretty much identical to SCSI. But Linux does not (yet) support that.
Cheers -- mlord@pobox.com
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