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Subject: Re: [RFC/RFT] calloutng
From: Ian Lepore <freebsd@damnhippie.dyndns.org>
To: Alexander Motin <mav@freebsd.org>
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Date: Sun, 13 Jan 2013 16:10:01 -0700
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Cc: Davide Italiano <davide@freebsd.org>, freebsd-arch@freebsd.org,
 FreeBSD Current <freebsd-current@freebsd.org>,
 Marius Strobl <marius@alchemy.franken.de>
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On Sun, 2013-01-13 at 21:36 +0200, Alexander Motin wrote:
> On 13.01.2013 20:09, Marius Strobl wrote:
[...]
> > 
> > Uhm, there are no NMIs on sparc64. Does it make sense to bypass this
> > adjustment on sparc64?
> 
> If it is not possible or not good to to stop timer during programming,
> there will always be some race window between code execution and timer
> ticking. So some minimal safety range should be reserved. Though it
> probably can be significantly reduced. In case of x86/HPET there is
> additional factor of NMI, that extends race to unpredictable level and
> so makes additional post-read almost mandatory.
> 
> >> May be with rereading counter
> >> after programming comparator (same as done for HPET, reading which is
> >> probably much more expensive) this value could be reduced.
> > 
> > I see. There are some bigger fish to fry at the moment though :)
> 

Speaking of the HPET code, it seems to me that its restart logic can
fire the same event twice.  Is that harmless?

-- Ian