Messages in this thread | | | From | "David Anderson" <> | Date | Tue, 04 Mar 2003 09:11:04 -0500 | Subject | Re: I/O Request [Elevator; Clustering; Scatter-Gather] |
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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 <axboe@suse.de> Date: Tue, 4 Mar 2003 14:50:00 +0100 To: David Anderson <david-anderson2003@mail.com> Subject: Re: I/O Request [Elevator; Clustering; Scatter-Gather]
> On Tue, Mar 04 2003, David Anderson wrote: > > > > 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 : > > > > 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.c and drivers/block/elevator.c. For 2.5, read > the same files and drivers/block/deadline-iosched.c in addition. > > > 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. > > -- > Jens Axboe >
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