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Date:      Fri, 21 Sep 2001 12:00:14 -0700 (PDT)
From:      John Baldwin <jhb@FreeBSD.org>
To:        Julian Elischer <julian@elischer.org>
Cc:        current@FreeBSD.org, Julian Elischer <julian@FreeBSD.org>, Jun Kuriyama <kuriyama@imgsrc.co.jp>, Dag-Erling Smorgrav <des@ofug.org>, Josef Karthauser <joe@tao.org.uk>
Subject:   Re: Problems with interrupts on -current.
Message-ID:  <XFMail.010921120014.jhb@FreeBSD.org>
In-Reply-To: <Pine.BSF.4.21.0109211156140.37053-100000@InterJet.elischer.org>

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On 21-Sep-01 Julian Elischer wrote:
> I must say I'm worried, but stumped..
> I cannot see this problem here, and I cannot think of a change in the 
> KSE support stuff that would have this effect.
> 
> There was soem small change in the statistics gathering code that
> is done at clock time, but nothing so low-level as to
> effect the further generation of clock ticks.
> 
> It does sound as thuogh statclock has been stopped though.

Really bad things can happen if another interrupt comes in during statclock and
causes a preemption.  In the preemptive kernel I had to wrap fast interrupt
handlers in a critical section.  I'll see if I can't resurrect that.
The problem is that during a fast interrupt handler, we don't acknowledge the
interrupt until we return from the interrupt handler, so if we preempt it may
be a while before we get back to the interrupted process so it can finish the
interrupt handler and ack the interrupt in the PIC.

-- 

John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

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