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

From: Segher Boessenkool
Date: Tue Jul 25 2006 - 19:24:09 EST

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)

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.


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