Re: GLIBC IA64 HP_TIMING fixes for SMP systems with unsynchronized

Christoph Lameter
2004-06-04T15:06:57Z

On Fri, 4 Jun 2004, Ulrich Drepper wrote:

> Christoph Lameter wrote:
>
> > clock_gettime(CLOCK_REALTIME) calls gettimeofday internally and then
> > multiplies with 1000.
>
> Internally where? clock_gettime is a syscall. And it can use whatever
> functionality the kernel provides. There is absolutely no requirement
> to add additional clocks, just make clock_gettime do the right think if
> this isn't happening already.

Internally in the kernel. Excerpts from kernel/posix-timers.c:

static int do_posix_gettime(struct k_clock *clock, struct timespec *tp)
{
struct timeval tv;

if (clock->clock_get)
return clock->clock_get(tp);

do_gettimeofday(&tv);
tp->tv_sec = tv.tv_sec;
tp->tv_nsec = tv.tv_usec * NSEC_PER_USEC;

return 0;
}

static u64 do_posix_clock_monotonic_gettime_parts(
struct timespec *tp, struct timespec *mo)
{
u64 jiff;
struct timeval tpv;
unsigned int seq;

do {
seq = read_seqbegin(&xtime_lock);
do_gettimeofday(&tpv);
*mo = wall_to_monotonic;
jiff = jiffies_64;

} while(read_seqretry(&xtime_lock, seq));

/*
* Love to get this before it is converted to usec.
* It would save a div AND a mpy.
*/
tp->tv_sec = tpv.tv_sec;
tp->tv_nsec = tpv.tv_usec * NSEC_PER_USEC;

return jiff;
}