Jan Kiszka wrote:
 > Gilles Chanteperdrix wrote:
 > > Jan Kiszka wrote:
 > >  > Gilles Chanteperdrix wrote:
 > >  > > Hi,
 > >  > > 
 > >  > > here comes, for review, a patch which reduces the overhead of
 > >  > > clock_gettime by directly reading the tsc in user-space for
 > >  > > architectures that support it.
 > >  > 
 > >  > Highly welcome. But I have one concern: How and when do you propagate
 > >  > wallclock_offset changes to user space?
 > > 
 > > Since clock_settime is not implemented, never, but if clock_settime was
 > > implemented, clock_settime would re-issue the __xn_sys_info syscall.
 > 
 > This excludes automatic clock adjustment, something I'm convinced we
 > will have to provide in the future.

When we provide automatic clock adjustment, we will have to devise
something more subtle than just an offset, so we will have to redesign
posix clocks support anyway. Maybe clock_gettime(CLOCK_REALTIME) will
then always be a syscall. After all, rt_timer_read is a syscall. If you
want the fast clock, use CLOCK_MONOTONIC or rt_timer_tsc.

-- 


                                            Gilles Chanteperdrix.

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