You should calculate your boards time drift and compensate for it. //Markus - The panama-hat hacker On 26 Oct 2016, at 10:55 , Deepak Gaur <dgaur@xxxxxxx> wrote: > 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 > >
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