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Subjectgettimeofday() in 2.6.24
Hi, I was trying to figure out how gettimeofday() measures time in
2.6.24-arm2, in which a free-running timer is added to improve the
resolution of gettimeofday() from 10ms to us, I can trace down to
do_gettimeofday() as follows:

http://lxr.linux.no/linux+v2.6.24/arch/arm/kernel/time.c#L240
239#ifndef CONFIG_GENERIC_TIME
240void do_gettimeofday(struct timeval *tv)
241{
242 unsigned long flags;
243 unsigned long seq;
244 unsigned long usec, sec;
245
246 do {
247 seq = read_seqbegin_irqsave(&xtime_lock, flags);
248 usec = system_timer->offset();
249 sec = xtime.tv_sec;
250 usec += xtime.tv_nsec / 1000;
251 } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
252
253 /* usec may have gone up a lot: be safe */
254 while (usec >= 1000000) {
255 usec -= 1000000;
256 sec++;
257 }
258
259 tv->tv_sec = sec;
260 tv->tv_usec = usec;
261}
262
263EXPORT_SYMBOL(do_gettimeofday);

but I haven't quite figured out how gettimeofday() actually gets time
from this added timer, also how xtime is updated?

Thanks, Jack


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