From owner-freebsd-current Mon Nov 13 21:55:31 1995 Return-Path: owner-current Received: (from root@localhost) by freefall.freebsd.org (8.6.12/8.6.6) id VAA28299 for current-outgoing; Mon, 13 Nov 1995 21:55:31 -0800 Received: from Root.COM (implode.Root.COM [198.145.90.17]) by freefall.freebsd.org (8.6.12/8.6.6) with ESMTP id VAA28292 for ; Mon, 13 Nov 1995 21:55:25 -0800 Received: from corbin.Root.COM (corbin [198.145.90.50]) by Root.COM (8.6.12/8.6.5) with ESMTP id VAA27737; Mon, 13 Nov 1995 21:55:24 -0800 Received: from localhost (localhost [127.0.0.1]) by corbin.Root.COM (8.6.12/8.6.5) with SMTP id VAA04329; Mon, 13 Nov 1995 21:49:49 -0800 Message-Id: <199511140549.VAA04329@corbin.Root.COM> To: Julian Elischer cc: uhclem%nemesis@fw.ast.com (Frank Durda IV), simonm@dcs.gla.ac.uk, current@freebsd.org Subject: Re: Disk I/O that binds In-reply-to: Your message of "Mon, 13 Nov 95 21:34:16 PST." <199511140534.VAA26450@ref.tfs.com> From: David Greenman Reply-To: davidg@Root.COM Date: Mon, 13 Nov 1995 21:49:48 -0800 Sender: owner-current@freebsd.org Precedence: bulk >however, a 5 Second wait would imply reading about 25MB of data! >(though I guess a process that neads to do 10 reads needs to get past this hog >10 times before being able to proceed (it might be getting little bits >of disk at a time. Only if you have very fast disks...which explains why people like me don't see the problem very often, and when I do see it, it's not serious enough to be a "problem". People with slow disks (IDE) will see the problem magnified significantly. For fairness, I think the queue depth for each chunk needs to be limited to less than 10 requests. It should be tuneable so that we can experiment with different values. For the moment I can write a patch that will disable the sorting in disksort - people experiancing the "hang" problem should try the patch when I make it available and see if the problem goes away. ...Of course disk performance will suffer unless you're using SCSI with tagged queueing (in which case the drive does the ordering - usually much more intelligently). -DG