From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266896AbTGHHlk (ORCPT ); Tue, 8 Jul 2003 03:41:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265525AbTGHHlk (ORCPT ); Tue, 8 Jul 2003 03:41:40 -0400 Received: from x35.xmailserver.org ([208.129.208.51]:18306 "EHLO x35.xmailserver.org") by vger.kernel.org with ESMTP id S266896AbTGHHlh (ORCPT ); Tue, 8 Jul 2003 03:41:37 -0400 X-AuthUser: davidel@xmailserver.org Date: Tue, 8 Jul 2003 00:48:36 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@bigblue.dev.mcafeelabs.com To: Daniel Phillips cc: Linux Kernel Mailing List Subject: Re: 2.5.74-mm1 In-Reply-To: <200307080307.18018.phillips@arcor.de> Message-ID: References: <20030703023714.55d13934.akpm@osdl.org> <200307080213.53203.phillips@arcor.de> <200307080307.18018.phillips@arcor.de> 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 On Tue, 8 Jul 2003, Daniel Phillips wrote: > 1. 400ms buffers are hated by users, as was noted previously. They are > passable for some applications, but way too laggy for others. > > 2. Even if you are will to have a 400-500 ms buffer, if you can prove that you > will always meet that deadline, then it's a realtime system. > > 3. If you can show logically that you will nearly always meet the deadline, > it's a soft realtime system. That's what we're after here. From a design > standpoint, there are elegant soft realtime systems, and there are sucky > ones. > > 4. So how do you propose to "program timings" so that it's really hard to miss > those deadlines? Having a backup of 400-500ms gives you an average hang-over of 200-250ms that are hardly noticeable by a human in this topic. The issue is not if you always meet the deadline, the issue is what amount of load will make you miss it. If I have to hire five ppl clicking and dragging on my desktop to make my player to skip, and it skips, I don't care if it missed the deadline. This because my desktop will hardly see that load. But if you have a 50-100ms backup, things turns out to be a little bit different. If you pretend to run a `make -jUNREAL` and still have the audio not skipping it is simply wrong. Running a `make -j20` in my machine shows an average of 24 TASK_RUNNING tasks, that even if they're granted with a mere 40ms timeslice, it'll take a full second before an expired task will see the light again. BTW, under such load RealPlayer skips badly, but I don't really care since it never did while I was doing all the normal (and many extra) stuff I'm doing on my desktop. - Davide