A Linux server running Ubuntu 12.04 LTS with LAMP has a strange behaviour since last week: - cpu %sys higher than before, nearly equal %usr (before that, %sys just little compare with %usr) - IO reduce by half or 1/3 compare with the week before

I try to diagnostic the process/cpu by some command (top/vmstat/mpstat/sar), and see that maybe it's a bit high on interrupt timer/resched. I don't know what that means, now open to any suggestion.