Subject: Re: [linux-audio-dev] What would YOU do with kernel support?
From: Will Benton (willb_AT_cs.wisc.edu)
Date: Fri Mar 22 2002 - 07:17:20 EET
On Thu, 2002-03-21 at 15:49, Paul Davis wrote:
> ALSA already has support for zero-copying I/O, via its mmap mode.
Thanks for your reply, Paul. I'm not as familiar with ALSA as I should
be, but I did know about mmap mode and its performance implications. I
hadn't assumed that the latency between application and hardware would
be the bottleneck, but rather that the latency between applications
would be.
I guess I should have been more specific: I was thinking that the
greatest benefits might be in zero-copying I/O for IPC, to support a
chain of filters/effects a la those in commercial programs like "Reason"
or similar.
Of course, that's irrelevant if all such viable systems use explicit
shared memory to pass data through different effects. (I personally
think that message passing or pipes are easier abstractions than shared
memory, but I realize that that's an unpopular view.) I guess that the
kind of application I had in mind was something like GNU Octal, but
development on that seems to have stagnated.
> scheduling latency is really the only issue i've every had
> with the kernel.
I just read one of the KURT papers
(http://www.ittc.ku.edu/kurt/papers/KURT-vienna-paper.ps). I agree;
dynamically introducing a different scheduling policy when applications
need it (or, as a first cut, ask for it) seems like the Right Thing to
do.
One interesting (but unfortunately likely irrelevant to audio) thing
that some dynamic optimization research has been aiming for lately is a
sort of bidding/guaranteeing mechanism. For example, an application
will ask for disk throughput of speed X mbps or N functional units in
the CPU, and the hardware/OS will be able to make guarantees about what
it can provide, so that the application will be able to modify itself to
work well under temporary resource constraints. This is mostly
applicable to devices that are power-constrained, but I've seen other
useful applications for it as well.
I suppose there might be an application for allowing an application to
specify a desired scheduler resolution (and receive feedback from the
kernel on what resolution it could actually supply), but I can't think
of one.
> --p <once, pbd_AT_cs.washington.edu>
:-) Actually, I believe I knew that; I've actually skimmed your Mach
threads paper. Oddly (or not) enough, I found it when looking for info
on using CPS in OS design. Ah, what you learn from arbitrary citeseer
traversals.
Thanks,
wb
-- Will Benton | "Die richtige Methode der Philosophie wäre eigentlich die: willb_AT_acm.org | Nichts zu sagen, als was sich sagen läßt...." **GnuPG public key: http://www.cs.wisc.edu/~willb/pubkey
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