[LAU] Question about DSP/Processor Load and multiproc support

Hello, I suppose this question has already been posted, and answered, but I can't get any explanation which seems to fit my question, or I do not understand it, so I post it there. I know that Jack DSP Load isn't a true DSP Load, it's nothing but buffering, if I'm not wrong. Though, I don't know what hardware part of the computer the DSP finally relies to (or affects, or whatever), but I suppose it's the processor, as the load of the DSP when launching, for example, one AMS seems to be the same as the processor load assigned to the AMS process. So, the first question is, does the DSP mean "processor load due to software appearing in jack"? Next, question is about multicore. When I monitor my system using top on a my quad-core or duo-core machines, I can reach total processor loads such as 400% or 200%, as top seems to be designed for monocore. Actually, it obviously means 4x100% or 2x100%. When I use Jack1, I got an Xrun (at least) every time I reach the 100% DSP load, which is finally with quite few softwares (4 AMS, 1 Sooperlooper, 1 seq24, 1 Tapeutape, some routing, some qmidiroute) for my configuration (Intel Q6600 Core 2 Quad, 8Gb RAM, Focusrite Saffire Pro 40 soundcard -firewire, with developpment version of FFADO-). What I was wondering is: does jack prefer to create an Xrun as soon as 100% DSP load is reached? I just installed jack2, in order to check whether it might increase the perf of my system, but, at first sight, the DSP load is the very same as with jack1. OK, here it is, I'm sorry it's not really clearly explained, it's quite clear in my head, but unfortunately, with french words!!! Thanks. -- Aurélien