Re: [PATCH] RTC: Add mmap method to rtc character driver

[Segher Boessenkool]

> > But userland cannot know if there is a more efficient option to
> > use than this /dev/rtc way, without using VDSO/vsyscall.
> Sure, but detecting if /dev/rtc via mmap is faster than  
> gettimeofday is an
> orthogonal issue to having the choice in the first place.

No it's not.  Userland can not detect things it doesn't know
about, and then when there is a great choice, it won't see it,
and use the 6000kW solution (or any other really bad thing)
instead.

Using the old old legacy stuff when there's nothing better around
is a fine idea; please just implement an x86 VDSO that does just
that.  x86 is what you care about IIUC.  Don't saddle up non-x86
systems that just happen to have a legacy RTC around, and perhaps
x86 systems that don't sanely expose their better interfaces, with
this quite suboptimal solution for years to come.


Segher

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