Date: Mon, 26 May 2003 13:49:57 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: Jens Axboe <axboe@suse.de>
cc: James Bottomley <James.Bottomley@SteelEye.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [BK PATCHES] add ata scsi driver
In-Reply-To: <20030526203800.GP845@suse.de>
Message-ID: <Pine.LNX.4.44.0305261345460.13489-100000@home.transmeta.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1226
Lines: 32


On Mon, 26 May 2003, Jens Axboe wrote:
> 
> I know this is a pet peeve of yours (must be, I remember you bringing it
> up at least 3 time before :), but I don't think that's necessarily true.
> It shouldn't matter _one_ bit whether you leave the request there or
> not, it's unmergeable.

It's not the merging that I worry about. It's latency and starvation.

Think of it this way: if you keep feeding a disk requests, and the disk 
always tries to do the closest one (which is a likely algorithm), you can 
easily have a situation where the disk _never_ actually schedules a 
request that is at one "end" of the platter. 

Think of all the fairness issues we've had in the elevator code, and 
realize that the low-level disk probably implements _none_ of those 
fairness algorithms.

> As long as the io scheduler keeps track of this (and it does!) we are
> golden.

Hmm.. Where does it keep track of request latency for requests that have 
been removed from the queue?

		Linus

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/