Hello, I have board with MIPS 34Kc processor and linux-2.6.29 with CONFIG_HZ_250=y set in kernel configuration (i.e 250 timer interrupts per 1 real second in /proc/interrupts). When I try to synchronize time using ntpdate command, the time gets synchronized. This resync is being done every 5 min using cron. The clocksource is set to jiffies and is the only source available. After some time (1 hr and more) the system clock (kernel/software) sometimes starts slowing down and sometime goes fast. System time increments very slowly i.e 1 sec on system takes 8-9 real seconds (as per wrist watch) or fast 2 sec in 1 real second. #date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:05 IST 2016 # date Tue Oct 25 15:14:06 IST 2016 # date Tue Oct 25 15:14:06 IST 2016 (It took 10 date commands to increment from 14:05 to 15:06) On further analysing the system we found the number of timer interrupts in /proc/interrupts has actually gone down from 250 to 40 every 1 real second (1) Normal Operation 10 real sec watch window cat /proc/interrupts Start of timer MIPS timer intr count 3856633 End of Timer MIPS timer intr count 3859268 Timing approximately 10-11 real sec, the interrupts are 263 per sec. (2) Clock Slow (Less Timer Interrupts) After ntpdate run for 1 hr once per 5 min cat /proc/interrupts Start of timer MIPS timer intr count 985072 End of Timer MIPS timer intr count 985492 985492 - 985072 = 420 in 10 sec (real) = 42 in 1 sec (3) Fast Clock with ntpdate (More Timer interrupts) Start of timer MIPS timer intr count 4068301 End of Timer MIPS timer intr count 4073411 985492 - 985072 = 5110 in 10 sec (real) = 511 in 1 real sec ntpdate uses ntp_adjtime()/adjtimex() GNU libc system call for changing system clock and can change it but by a very small amount. But the issue is it is changing system clock so much that other application have started behaving erratically, timers are not expiring in required time etc.. and once the system clock has slowed down/fast it remains in that state. # cat /sys/devices/system/clocksource/clocksource0/available_clocksource jiffies # cat /sys/devices/system/clocksource/clocksource0/current_clocksource jiffies We are using gcc version 4.5.2 and gnu libc Please help me in understanding this behaviour of NTP with MIPS Linux and possible fixes if any. Is it a kernel bug or a configuration issue? regards, Deepak Gaur
