Would be really really nice to have measures by thread id, so we can distinguish mainthread IO from other threads IO, both are bad but the first one is immediately visible to the user.

This bug has been around for almost 4 years, if we don't plan to work on it in the next couple of months, I would like to close it out. Please speak up if there are reasons to keep it open.

I think this might have already been added as part of my previous xperf work anyway, so I suggest that we just mark it as fixed.

bug 644744, to be exact.