OK guys, I give up.
CS6 on a MacPro tower.
2x2.4 Ghz quad Xeons,
14 Gb ram,
ATI Radeon HD 5770 with 1GB Vram
Primary drive (scratch1) is an SSD, about 40Gb free. Secondary scratches on several externals with multiple Tb available.
MacOSX 10.9 (up to date as of 7/24/14)
Pair of generic NEC monitors.
12" Wacom Intuos tablet. (Drivers up to date.)
Kensington trackball (Drivers up to date)
I use Photoshop intermittently these days, so I'm not sure when the problem started, but I go back to PS2, (on floppies.) so this isn't a basic 'noob doesn't know what he's doing' issue.
Problem: PS6 starts out OK with the brush tool (in quickmask, for painting in a mask) or with the clone stamp tool for patching. (Seems to happen with any of the brush-like tools, but those are the ones that I use most, so that's what I noticed.)
Works fine for a bit, but gradually slows down, and eventually gets to the point where the brush is lagging *minutes* behind my clicks. Eventually just locks up solid. The fun part is that as it's slowing down, it will sometimes randomly pick new locations to record a click, so after it gets to the point where I'm waiting to see when/if it'll catch up, suddenly a series of zig-zags will turn up, totally destroying whatever mask I was working on. I tend to work by way of doing shift-click to get large areas nailed, so it isn't like it's recording a lot of location data, it's just 'point-move-point'. (I've got the pressure sensitivity of the Wacom turned off, so it's not even bothering with that. It really is pure XY data, and not much of it.)
It gets really flaky if I reposition the viewport while it's getting slow. Looks sort of like it picks a spot kinda-sorta-close to where my most recent click would have been if the viewport had been in the old location, and then works from there, so I get streaks going all over the place. It also loves to draw straight lines heading off the primary screen if I move the pointer over onto the secondary monitor. (all the pallets are over there.) I tend to go over there to get ready to step back a few history states as soon as it unfreezes, because the last few brushstrokes are guaranteed to be mispositioned garbage.)
I've got the GPU stuff totally turned off, and that made no difference on any setting. Updated the Wacom and Kensington drivers. No difference. PS has about 8gb of RAM, operating at 100% efficiency. File sizes are in the range of 64-128 Mb, but that doesn't seem to make any real difference. Lightroom 5 is usually running in the background, and maybe iTunes and mail, but that's it. I've got a quick-key rigged to dump all the PS caches and buffers. Doesn't help. The only solution is to grit my teeth and use it until it chokes, and then force-quit and start over. Clearly, this way lies madness. (Or a different (non CC) graphics program.)
I first noticed it after the 10.9 upgrade, so it may be some weirdness with 10.9, but I can't figure what. It looks like it's having trouble with keylogging, and there's a memory leak somewhere.
Anybody have any clues? It's pretty much useless as it is, an I've got work I need to get out.