Messages in this thread |  | | | From | laredo@gnu ... | | Subject | Re: Guaranteeing processing speed... | | Date | Wed, 13 Oct 1999 14:59:44 -0400 (EDT) |
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> Suppose you have a process that needs a certain amount of CPU power. > Think of > an MPEG player showing a movie. If you start other processes absorbing a > lot of > [...] > BogoMIPS or whatever). When the OS isn't able anymore to grant the > requested > amount of processing speed to the process, it could inform it by sending > a > signal. Then the process could decide upon what to do. The MPEG player, > e.g., > could skip every second frame. > > Is this out-of-realm for Linux? Is it a typical problem for an RT-OS?
I think this is silly personally. A well-written MPEG player will be able to track its performance for each frame and drop as necessary. This means that regardless of the load it should always be able to stay in perfect sync. Why is this important? Well when you get into variable bitrate sources such as DVD, your processing power required is NOT a constant. Various tricks may be employed such as watching the clock and using the "rdtsc" instruction to get as accurate timing as possible. Of course when APM is enabled, you can really throw things off as the "hlt" instruction might be executed and your rdtsc will be off.
Anyway the short of it is that you should just be watching the system clock and ensuring that your audio and video are delivered at the specified delivery times in the stream and skipping frames or varying the audio sample rate if necessary.
-- Nathan Laredo laredo@gnu.org
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