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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