Messages in this thread | | | Date | Tue, 28 Dec 2010 17:35:22 +0530 | Subject | Drift when measuring time using add_timer | From | Mohan V <> |
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Hello All,
I am testing the timers on a OMAP4 based board. I am seeing a drift or the time difference between the timer value and when the function callback happens. This drift is around 1000ms or 1s for a expiry value of >=5mins. Is the time drift expected? Is this way of measuring right or is there any other way?
OMAP4 as you may know is a multi-core processor and CONFIG_SMP is enabled along with the following: CONFIG_NO_HZ, CONFIG_HIGH_RES_TIMERS
My kernel configurations: kernel: 2.6.37-rc7 (commit id: ffc96d) config: omap2plus_defconfig
My driver does the following:
struct timeval tv; test_timer_proc_write() { del_timer_sync(&my_timer); period = 300000; /* 5min */ my_timer.expires = jiffies + msecs_to_jiffies(period); my_timer.function = func_timeout; /* Call back function*/ /* Save the current time in global variable */ do_gettimeofday(&timeval); /* add timer with an expiry value of 5mins*/ add_timer(&my_timer); }
/* Get the current time and print the difference between the two values */ func_timeout() { struct timeval tv1; do_gettimeofday(&tv); /* take the difference between current time and saved time */ ms = (tv.tv_sec - tv1.tv_sec) * 1000 + \ (tv.tv_usec - tv1.tv_usec) / 1000; printk("Interval = %d\n", ms); }
Thanks for your time.
Regards, Mohan
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