Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 6 Sep 2002 02:54:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 6 Sep 2002 02:54:07 -0400 Received: from neon-gw-l3.transmeta.com ([63.209.4.196]:49425 "EHLO neon-gw.transmeta.com") by vger.kernel.org with ESMTP id ; Fri, 6 Sep 2002 02:54:06 -0400 Date: Thu, 5 Sep 2002 23:59:10 -0700 (PDT) From: Linus Torvalds To: Helge Hafting cc: linux-kernel@vger.kernel.org Subject: Re: One more bio for for floppy users in 2.5.33.. In-Reply-To: <3D784F8A.CE0CF1DB@aitel.hist.no> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2248 Lines: 52 On Fri, 6 Sep 2002, Helge Hafting wrote: > > I can think of one case where large readahead hurts for floppy, even > with partial completion: > > 1. Grab a stack of floppies > 2. Try mounting (or mount+ls) one after another, > in search of the right one. Note that the delay for motor on/off is _much_ larger than the actual delay for seeking. The seek itself is on the order of a few ms, with the head settle time being in the tens (possibly even a few hundred) ms per track. So assuming you end up reading 4 tracks or so due to readahead, that's still in the range of about one second. In contrast, the motor on/off time is something like 5 seconds if I remember correctly. Of course, you can certainly eject the floppy while the motor is still running, but I'd suggest against it. > So I think a smaller readahead might make sense for floppies, > unless people don't do this sort of search anymore. I don't. I do agree that a 64kB readahead is likely to be excessive on a floppy, I'm just saying that I doubt it will be all that noticeable in most cases. The absolute worst case is when opening, reading a sector, and closing again several times in succession, at which point right now we'll end up serializing. But even at 64kB, that's going to be faster than most people can change floppies if they actually want to even glance at what the contents are. The reason I want the first sectors to be returned early is that I thought it was quite noticeable to do just a simple "ls" on the floppy when I tested. Of course, that may be just me: it's literally been several years since I really used floppies, and maybe they really always were that slow. But I thought the root directory was on track zero, so it _should_ return it first thing. Oh, well. I don't seem to be the only one who doesn't use the dang things any more. The floppy driver has been broken in 2.5.x for half a year or whatever, and there weren't _that_ many people who ever even mentioned it. 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/