From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David Anderson" Subject: Re: I/O Request [Elevator; Clustering; Scatter-Gather] Date: Tue, 04 Mar 2003 09:11:04 -0500 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20030304141104.65579.qmail@mail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline List-Id: linux-scsi@vger.kernel.org To: axboe@suse.de, david-anderson2003@mail.com Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org 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 Date: Tue, 4 Mar 2003 14:50:00 +0100 To: David Anderson 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 > -- __________________________________________________________ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup