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

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Date:	Tue, 25 Jul 2006 13:24:58 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Airlie <airlied@...il.com>
CC:	Neil Horman <nhorman@...driver.com>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, a.zummo@...ertech.it,
	jg@...edesktop.org
Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver

Dave Airlie wrote:
> 
> So far the requirements are pretty much not high resolution but is
> accurate and increasing. so like 10ms is fine, the current X timer is
> in the 20ms range.
> 
> I think an mmap'ed page with whatever cgt(CLOCK_MONOTONIC) returns
> would be very good, but it might be nice to implement some sort of new
> generic /dev that X can mmap and each arch can do what they want in
> it,
> 
> I'm wondering why x86 doesn't have gettimeofday vDSO (does x86 have
> proper vDSO support at all apart from sysenter?),
> 

The i386 vdso right now has only two entry points, as far as I can tell: 
system call and signal return.

There is no reason it couldn't have more than that.  A low-resolution 
and a high-resolution gettimeofday might be a good idea.

	-hpa

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