smp questions etc

[Gustin Johnson]

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This is a pretty complicated question.  There is overhead with Multiple
CPUs, but a multi threaded app on a multi CPU machine can have a
positive impact on memory latency.  There are also differences between
AMDs HyperTransport and the "legacy" FSB of Intel.

Windows 2000 & XP used to have serious latency issues as a result of its
HAL (hardware abstraction layer) and certain hardware drivers.  I have
not used Windows as a DAW since 2003, but I remember it was a pain
getting latencies down in a stable way.  I have also since replaced my
hardware so I am probably not all that qualified to comment on this.

Then there is the software itself, with how DAWs work under Windows and
Linux. The alsa + jack combo is pretty nifty but has no real equivalent
under windows AFAIK.

Personally I don't think that cost benefit ratio warrants the more
expensive CPU.  I do most of my work on an AMD 939 dual core with
regular DDR RAM and I don't feel the need to upgrade.  Otoh, I don't
have to worry as much about FSB speed with my AMD.

Of course this is all just my opinion, I would encourage you to research
this yourself.

Use google to search http://lkml.org for starters.
The 64studio forums might not be a bad place to look either.
http://jackit.sourceforge.net/docs/faq.php#a51

Btw, the RME 9652 is a pretty sweet card, I have it running in a
64studio box right now with an ADI-8 DS and two older ADATs when I need
more channels.

Hth,


Jonathan Leonard wrote:
> On Aug 20, 2007, at 7:04 PM, Matthew Polashek wrote:
> 
>> Ok, I'm throwing together a new box in which I will install  
>> UbuntuStudio with the intention of using it as a live processing  
>> rig for live performance using PD.  I'm interested in discovering  
>> whether it makes more sense to get a Core 2 Quad processor that  
>> runs with a bus speed of 1066 or a Core 2 Duo processor that runs  
>> with a bus speed of 1333.  The idea is to reduce latency as much as  
>> possible.  I'll get I/O via a RME 9652 and a couple Behringer  
>> ADA8000 units.  Also, any thoughts on how ram speed plays into this  
>> equation?  I'm looking at the Intel dg33fb board.
> 
> Hi Matt, have you checked out www.dawbench.com?  While that site does  
> not specifically deal with linux, it has a lot of information and  
> test results comparing daw performance over a range of processor  
> counts and buffer sizes.  There is some contention about the utility  
> of multiple processors or core for low latency needs because of the  
> overhead in syncing and managing more than 1 cpu.  Some developers  
> claim that with smp 10 ms is the effective lower limit because below  
> this you waste cpu.  Its a shame because most new hotrod machines are  
> multicore.  IIRC from that site, there seems to be some benefit in  
> having dual core, but less and less as you go up - for low latency  
> use where you really have to work at 8ms or less.  As a rule it is  
> not my impression that adding any more cpu or core will help latency,  
> but perhaps make it worse.  But I too am learning about this in linux  
> and maybe things are entirely different.
> 
> If anyone has additional information to share regarding low latency  
> SMP in linux and the application of 'computer as musical instrument',  
> I would also really appreciate this!
> 
> Thanks,
> 
> Jonathan Leonard
> 
> 
> 
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