My RMBP becomes very slow after I upgrade yosemite

I bore this problem for a long time. I even formatted my disk and have a clean installation. However, this problem does exist.

After I boot my RMBP, everything is fine. I can drag every thing, every window smoothly. When I use this computer for hours, however, every thing becomes slow. Sometimes, there is a long response after I hitting a key.

I always use RMBP with an external monitor -- a dell display. And it seems that after awaking from a long time sleep, situation gets worse.

Is there anyone has the familiar problem? How can I fix it?

I now waiting for 10.10.2, I hope this patch could solve my problem.

By the way: I tried reinstall Mavericks and the problem gone away. However, I prefer the Yosemite theme very much, so, I don't want to roll back. $_$