Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 08 Jul 2003 19:18:20 +1000 | From | Nick Piggin <> | Subject | Re: 2.5.74-mm1 |
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Davide Libenzi wrote:
>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. > >
I agree some people have some inflated ideas about a desktop workload, but I'd just point out that if your mp3 player was using say 2% CPU, it should be able to preempt the make soon after it becomes runnable, and not have to wait at the end of the queue. It would become a CPU hog itself if you had 48 other processes running though.
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