Messages in this thread | | | Date | Mon, 14 Jan 2002 13:11:24 -0800 | From | Andrew Morton <> | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable |
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Alan Cox wrote: > > > I have all along assumed that a well-designed RT application would delegate > > all these operations to SCHED_OTHER worker processes, probably via shared > > memory/shared mappings. So in the simplest case, you'd have a SCHED_FIFO > > task which talks to the hardware, and which has a helper task which reads > > and writes stuff from and to disk. With sufficient buffering and readahead > > to cover the worst case IO latencies. > > A real RT task has hard guarantees and to all intents and purposes you may > deem the system failed if it ever misses one (arguably if you cannot verify > it will never miss one).
We know that :) Here, "RT" means "Linux-RT": something which is non-SCHED_OTHER, and which we'd prefer didn't completely suck.
> The stuff we care about is things like DVD players which tangle with > sockets, pipes, X11, memory allocation, and synchronization between multiple > hardware devices all running at slightly incorrect clocks.
Well, that's my point. A well-designed DVD player would have two processes. One which tangles with the sockets, pipes, disks, etc, and which feeds data into and out of the SCHED_FIFO task via a shared, mlocked memory region.
What I'm trying to develop here is a set of guidelines which will allow application developers to design these programs with a reasonable degree of success.
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