Re: Benefits from computing physical IDE disk geometry?

[Nick Piggin]

Chuck Ebbert wrote:

>>The way you would do a good "goodness" function, I guess,
>>would be to search through all requests on the device, and return
>>the minimum distance from the request you are running the query
>>on. Do this for both queues, and insert the request into the
>>queue with the smallest delta. I don't see much else doing any
>>good.
>>
>
>
>  That would be perfect.  And like you say in a later message, they're
>in a tree so it might actually work.  Then the read balance code
>wouldn't need to do that calculation at all.
>
>  How hard would this be to add?
>
It would be easy to add. Though of course it would have to
be shown to give an improvement somewhere to be included.

>
>
>
>
>>On the other hand, if you simply have a fifo after the RAID
>>scheduler, the RAID scheduler itself knows where each disk's
>>head will end up simply by tracking the value of the last
>>sector it has submitted to the device. It also has the advantage
>>that it doesn't have "high level" scheduling stuff below it
>>ie. request deadline handling, elevator scheme, etc.
>>
>>This gives the RAID scheduler more information, without
>>taking any away from the high level scheduler AFAIKS.
>>
>
>
> But then wouldn't you have to put all that into the RAID
>scheduler?
>
No - as far as I can see, the RAID scheduler already does
this. Having FIFOs between it and the disks would simply
make its assumptions valid.