Subject: Re: Disk scheduling policy (Re: NEW_BUFQ_STRATEGY)
To: Jason Thorpe <>
From: Alfred Perlstein <>
List: tech-kern
Date: 12/01/2003 15:04:58
* Jason Thorpe <> [031201 14:00] wrote:
> On Dec 1, 2003, at 12:07 PM, Thor Lancelot Simon wrote:
> >| In 6.5.8, the queues are split. Doing this permits queuing delayed 
> >writes
> >| into one queue, while synchronous writes and reads are entered into 
> >another
> >| queue. In 6.5.8 the disk driver will alternate between queues. This 
> This is a pretty cool, and fairly simple, algorithm.  I bet it could be 
> implemented as a back-end to the new bufq code pretty easily.

If you keep the bufs on two queues, a combined queue and seperate
queues you'll pay double the sorting cost, but only have to disrupt
the elevator algorithm when you reach a tuneable threshold.  In fact
you could keep a single queue and split it when the io becomes
too saturated as well by keeping counts of the mix in the single

- Alfred Perlstein
- Research Engineering Development Inc.
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