I/O Request [Elevator; Clustering; Scatter-Gather]
Hi,
Thanks a lot for the reply...
I am using linux 2.4.
Got mislead with the statement in "Linux Device Drivers"
"Most high-performance disk controllers can do “scatter/gather” I/O as well, leading to large performance gains."
Thanks and Regards,
David Anderson
----- Original Message -----
From: Jens Axboe <[email protected]>
Date: Tue, 4 Mar 2003 14:50:00 +0100
To: David Anderson <[email protected]>
Subject: Re: I/O Request [Elevator; Clustering; Scatter-Gather]
Quoted 30 lines · David Anderson
Quoted 5 lines
Hi, I have been going through some documentation that talks of clustering, scatter-gather and elevator being used to improve performance. I am confused between these :
Quoted 8 lines
This is what I have understood : Elevator The job of the elevator is to sort I/O requests to disk drives in such a way that the disk head moving in the same direction for maximum performance. Have been able to locate the code for the same.
Clustering Combines multiple requests to adjecent blocks into a single request. Have not been able to find the code which carries this out. Any clue on where this is done in the linux source code ??
Both actions are performed by the elevator in Linux. You did not mention which kernel you are looking at, for 2.4 you need to read
drivers/block/ll_rw_blk.canddrivers/block/elevator.c. For 2.5, read the same files anddrivers/block/deadline-iosched.cin addition.Quoted 2 lines
Do Clustering of request and scatter-gather mean the same ?? Confused to the core... Kindly help me ...
No, the elevator clustering refers to clustering request that are contigious on disk. Scatter-gather may cluster sg entries that are contigious in memory.
Signature · 1 line
Jens Axboe
Signature · 3 lines
__________________________________________________________ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup