I had been running Kernel 4.2 on my main system since it was released, but have been experiencing vague and inconsistent problems with sluggish applications, which sometimes hung for about half-a-second..   Nothing specific, and no apparent errors reported..

I reverted to Kernel 4.1.7, and everything seems to be back to normal..   I will try 4.2.1 as soon as it is available..

Robert Gadsdon.   September 14, 2015.