Audio/Video Problems

[Mark Greenwood]

On 3 Jan 2013, at 19:54, Gene Heskett wrote:

> On Thursday 03 January 2013 14:44:13 Mark Greenwood did opine:
> Message additions Copyright Thursday 03 January 2013 by Gene Heskett
> 
>> On 3 Jan 2013, at 18:20, Gene Heskett wrote:
>>> I guess what I wanted to say was that for some uses, the latest and
>>> greatest, because its real world performance sucks dead toads thru
>>> soda straws, is a disaster.
>> 
>> Couldn't agree more Gene :) I use Linux for music production
>> (occasionally) and need hard real-time performance. Things have been
>> getting steadily worse since 10.10 and the latest release is completely
>> useless to me. (Audio latency minimum I can get is 200ms, as opposed to
>> 5ms with 10.10).
>> 
> Yee Gods! And keep in mind even the 5ms of 10.10 takes it totally out of 
> the running for us. There is no film at 11 for that, not even faked on 
> youtube.
> 
>> However I don't think (K)Ubuntu are to blame for this, it's entirely in
>> the hands of the kernel developers and Linus himself has no interest in
>> realtime.
> 
> That too, and has been so noted in the discussions I have "copied the mail" 
> on.  We have, over the last 6 months as this deadline looms on the horizon, 
> investigated the other guys, bsd, qnx et all and found them equally and 
> deadly lacking in something so damned simple as a context switch to handle 
> an IRQ in at least a repeatable amount of time.  We don't have the 
> resources to sit down and write our own kernel, but it has been discussed.

The best realtime system I ever had (on *any* OS, I've used MacOS and various versions of Windows over 15 years) was based on Mandriva 2008 (I think) with a kernel.org 2.6 series kernel (I'm sure about the 2.6) with Ingo Molnar's realtime patches. On that system I had 1ms latency, although I had to increase it to 4ms to make it stable under heavy disc load (and I mean getting close to maxing out a 3GB/s bus while running 32 tracks of drum sequencer, 16 audio tracks, and overdubbing in stereo. The sort of thing people pay tens of thousands for when they buy professional digital mixing desks). And all that on a 2GHz processor with 2G of RAM. Windows would't even have got a look in. Things have gone downhill ever since. Bear in mind that audio latency relies on transmitting multiple very (relatively) large buffers in two directions. Less CPU-intensive applications (such as CNC) would do much better. But these days, on the same hardware, Linux with a Firewire sound card gets p*****d all over by Windows 7, even when I make it hard for Windows by using USB sound hardware. It's quite sad. I bought a Mac 2 years ago and that now gets used for anything important because it works without me having to fight with it.

To be fair to Linux, Linus has been quoted as saying something along the lines of 'it was never designed or intended for realtime use. If anybody wants to use it for such applications then good luck to them but they're mad'.

Try a 2.6 series kernel, add Ingo Molnar's patches, switch off all the kernel debugging options, enable Message Signalled Interrupts, HPET, and set the timer frequency to 1000Hz. It worked wonders for me.

Mark

> 
>> Mark
> 
> Cheers, Gene
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