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.
>
> I think we need some vsyscall-alike approach for this, some read-only
> page that is mapped into every RT process, containing things like a
> regularly updated offset (seqlock fashioned) or other read-only
> information (shadow mode? cpu id?).
As I said yesterday, having a page mapped at a different address in
kernel-space and user-space is not an option on ARM, because each
mapping of this page would have a separated cache.
--
Gilles Chanteperdrix.
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