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SubjectRe: disk head scheduling
On Wed, 24 Mar 1999, Gerard Roudier wrote:

> You only thought IDE and it what I pointed out, btw.
> For SCSI with 1 queue per device, if we are globally plugged we lose
> time (think of SMP, and interruptions), and if we discard the plug, we
> may break the coalescencing and sorting, and then just provide devices
> with bunches small IOs.

I admit that not implementing per-queue plugs at that time was a mistake.
The time in which the plug is being held should be very short relative to
actual I/O times, though, just enough to let the higher layers complete
putting all those small requests and colaescencing them, which is a
CPU <--> memory operation.



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