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SubjectRe: [alsa-devel] AMIGA will use Linux, but Linux has several "multimedia-deficiencies"
I used to have an Amiga (well I still have it actually, my brother still
plays my old games on it). What I wonder about is what hardware the new
Amiga's will have. My 500 had a 7.xx Mhz Motorola 68000 but it still wiped
the floor with a PC. It did (kind of) multitasking and was 32-bit. But
what made the computer by itself so great was the extra chips the thing
had. The special DMA, Video, Sound, ... chips did a lot of neat stuff.
E.g. chip-RAM was shared between CPU and that big DMA-chip (can't remember
his name :) ) makeing it so that a lot of stuff could be handled without
the CPU haveing to come into the picture.

So I think I'd like to know what hardware they'll use before I'd start
makeing a fuss. If I gave you a DSP that did mp3-decoding (costs near to
nothing BTW) your CPU would need to do nearly nothing to play an mp3 (a
286 would be enough). For many other things this goes too. It shouldn't be
too hard to put in some DSP's that do some neat tricks and make everything
a lot easier to handle. AFAIK short latency is interesting because you
want to make small blocks of data so you have instant changes in your
output. But if you'd move a big part of that functionality to a DSP you'd
have a lot less worries.

Another thing for your tests:
- I know you've tested more recent kernels but did you remember to remove
update in your rc-scripts? You should check in pstree wether you only see
kflushd or both kflushd and update. update shouldn't be there as update
works somewhat differently than kflushd and will disturb eachother because
they are both there for te same task: getting buffered data to disk.

Dirk Moerenhout ///// System Administrator ///// Planet Internet NV

On Sat, 10 Jul 1999, Benno Senoner wrote:

> Hello,
>
> I've just read that the next generation AMIGA will use Linux as the core OS,
> instead of QNX. ( http://www.amiga.com/diary/executive/linux-e.html )
>
> Amiga is a multimedia platform, and therefore needs realtime capatibilites.
>
> Unfortunately actually Linux doesn't allow to play any realtime
> (low-latency) mulimedia content (audio/video,etc.) in a reliable fashion
> , during high system load, especially disk I/O.
> I was very disappointed when I benchmarked a 130ms max scheduling latency of a
> realtime scheduled audio process (playing from RAM) under high disk I/O load on
> my PII400 + 16GB UDMA harddisk. (for infos see my latency benchmark page)
> Even Win98 is able to get 17ms audio latency on my machine (during
> heavy disk I/O) without many problems.
>
>
> It's a bit disappointing that under Linux we get latencies which are
> 50-100times the realistic (<5ms) latencies, we are FAR AWAY from the hardware
> limits.
>
> I was shocked when disabling DMA on my HD, my realtime process was
> not rescheduled for *4000ms* = 4sec !
> (a 100m sprinter is able to run 35m in the same time :-) )
>
> Not only the audio layer is affected but many other subsystems too.
> For example benchmarking usleep() I noticed a max 100-150ms scheduling
> latency during high disk I/O load.
> I don't understand why a process should block occasionally up to 150ms , when
> usleep()ing only a few ms, because of the high disk I/O.
>
> Actually there seems not a big interest to cure these deficiencies, just
> because many see Linux as a server OS , and not a desktop OS,
> on a web-server or fileserver you don't need guaranteed timing.
> (Or is there already some unoffical work underway to cure the scheduling
> problems of Linux ?)
>
> Who cares if his webpage shows up 150ms earlier or later ? ,
> or if your netscape executable which comes from the NFS server, is loaded
> 150ms later ? No one, I think.
>
> Does anyone know if the disk device driver (or device drivers in general) can be
> preempted from regular processes or is there no way to do this on Linux.
> Do we really need a microkernel to handle realtime multimedia ?
>
> Hopefully Amiga Inc, will help us to optimize these Linux deficiencies, through
> collaborating with the kernel/audio/video developement folks.
>
> comments ?
>
> regards,
> Benno.
>
> Benno Senoner
> E-Mail: sbenno@gardena.net
> Linux scheduling latency benchmarks
> http://www.gardena.net/benno/linux/audio
>
> ------
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> 'unsubscribe' in the body of message to <alsa-devel-request@alsa-project.org>.
>


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