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Recently I have noticed that when I return to my computer after it has been "locked" for a while, the mouse pointer has significant lag. The cursor position appears to only update a few times a second. Moving the mouse results in the pointer "following" the movement in a jerky kind of way, and then continuing for some fraction of a second after I have stopped using the mouse.

Replacing the mouse has no effect. (I have two differently branded and constructed usb optical mice). Plugging either mouse into a different usb port has no effect.

Once the problem was resolved by "suspending" the system, and then re-starting it with the power switch, but this does not work every time. So far, the only fool-proof fix is to shut the system down and re-start it (re-boot).

I have tried this suggested fix. It had no effect.

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This problem affects ALL USB 2.0 devices attached to my system. When performance is normal, I can copy files from a USB 2.0 card reader to my desktop at 16MB/s. When the problem manifests, I can only copy at 450kB/s. USB scanner performance is acceptable after boot, miserable when the problem manifests. –  Bill Jones Jan 6 '13 at 19:12
    
FWIW, I've had this problem when I had a bad USB hub. Even if it's on another port, it's the same BUS. For the purposes of experimenting, what happens when only the mouse is plugged in, and nothing else in any USB port? –  Ken Jan 19 '13 at 0:06
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1 Answer 1

After months of this recurring problem, I believe I have finally found the cause:

Intel Sandy Bridge GPU power management - when i915 rc6 is enabled, I get occasional USB slowdowns after resuming from a lock screen. With it disabled, the symptoms are gone for good.

Here's precisely what I did: Edited the file /etc/default/grub to include the line

GRUB_CMDLINE_LINUX="i915.i915_enable_rc6=0"
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