I am on a brand new 12-core (dual 6-core 2.66GHz) Mac Pro with 16GB of RAM (and of course running 10.6.4). I have a new install of CS5 Master Suite (trial version, our box has not arrived yet), and primarily in my explorations with After Effects, it is running PAINFULLY slowly, mostly around simple interface stuff like scrubbing the timeline.
But this was also very apparent during rendering - a project that took about 20 minutes on my old 32-bit Core 2 Duo Dell with 4GB of RAM and CS4 took about 14 minutes on this new one under CS5 (running with 4 cores each using 2GB of RAM, and plenty of cores and RAM left over for other system stuff)... but I could see that a lot of that was due to HUGE delays in processing time as it rendered, long swaths of spinning beach-ball time. Had it not been for those, it likely would have rendered in about 2-3 minutes (as I would expect).
I have installed all available system and Adobe updates as of today (9/28/10), I am now running the updated AE 10.0.1... and I am having the same issues, with AE running very, very slowly. Scrubbing a project is nearly impossible - it regularly sends the system right to the beach-ball for many seconds; opening one project, which took 7-15 seconds on the Windows side (an old 32-bit Core 2 Duo Dell with 4GB Ram and CS4), takes up to 4:30 on the Mac under CS5! Same project, hierarchy, footage, etc.
I tried rendering it several ways: with 2 cores with 3GB each (leaving 6GB and 12 cores for other apps), with 3 multiprocessor cores each with 3GB of RAM (leaving 4GB of RAM and 10 cores for other apps), with 4 cores with 2GB each (6GB and 12 cores allowed for other stuff), with 7 cores each with 1.5 GB (leaving the minimum RAM and cores for other apps) and with NO multiprocessing on at all. Just for the baseline, the old Dell rendered this same file in 23:49, so all of these results are an improvement over that, but not nearly enough! Those long pauses still occurred - while watching the render, I could see it fly through parts, and then choke for many seconds at a time. Here are the timing results:
Multiprocessing Off: 9:57
2 Cores with 3GB each: 14:01
3 Cores with 3GB each: 9:36
4 Cores with 2GB each: 9:12
7 Cores with 1.5GB each: 15:12
This all seems pretty *******' random, though my testing methodology was far from iron-clad, as you can see. But either way, you would think with my system specs more cores would produce better results, not worse. I would have expected the 2 or 3 core configs to produce the best results.
The horrible lags seemed most pronounced on frames that cross faded, even a very simple crossfade - there was only one of significance in my video, where two videos crossfade over the space of about a second; each FRAME of that crossfade appeared to take about 20-30 seconds to render... or more accurately, each frame would render, and then there would be one of the insane processor lags. No lags this bad or pronounced happened on the Dell side - it was slow all around, but consistent.
Now, I did some tests with Activity Monitor open, and discovered some interesting things. When rendering with multiprocessing, each core used for rendering shows up as a process called "aeselflink" (as I'm sure you know), and at least a few of them are always at the top of the list, if you view activity by % CPU.
What was interesting is that while the render was actually processing (I could see motion in the render preview, as opposed to when it was choked), the CPU usage graph looked as you'd expect, going up and down between 5-50% of the CPU use. But when it stalled out and choked on a frame - or whatever it was doing - the CPU usage in the graph would PIN to the top as completely maxed out, with between 98 and 99% of the usage going to % User.
When those lags happened, the aeselflink processes often showed up as EACH using anywhere from 200% to 900% of the % CPU. Sometimes they were all pinned up there; other times only one or two seemed to demand that much time. Sometimes, however, things choked and the CPU usage graph showed NO activity, plain black idle for many seconds at a time. This doesn't seem to reveal much to me, but maybe smarter people can get some info from it.
Also, sometimes when starting a render, the aeselflink processes would show up in the Activity monitor normally, not demanding much time, but for a good long time (1-2 minutes) the main AE application process would show up red, saying it was not responding; during this time, the CPU usage graph showed almost no activity at all, just 0-10% User activity.
Whew. Ok, there's my random smattering of data. I hope this helps give someone in the know a better picture of what's going on here... this is a huge problem if it can't be addressed.