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Date: Sun, 11 Feb 2001 12:14:39 +0000
To: Pavel Machek <pavel@suse.cz>
Cc: Andrew Morton <andrewm@uow.edu.au>, Hacksaw <hacksaw@hacksaw.org>,
        Tom Eastep <teastep@seattlefirewall.dyndns.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [OT] Major Clock Drift
Message-ID: <20010211121439.A1039@colonel-panic.com>
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	Andrew Morton <andrewm@uow.edu.au>, Hacksaw <hacksaw@hacksaw.org>,
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	linux-kernel@vger.kernel.org
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In-Reply-To: <20010211120614.E23048@atrey.karlin.mff.cuni.cz>; from pavel@suse.cz on Sun, Feb 11, 2001 at 12:06:14PM +0100
From: Peter Horton <pdh@colonel-panic.com>
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On Sun, Feb 11, 2001 at 12:06:14PM +0100, Pavel Machek wrote:
> 
> > > > > >I've discovered that heavy use of vesafb can be a major source of clock
> > > > > >drift on my system, especially if I don't specify "ypan" or "ywrap". On my
> > > > >
> > > > > This is extremely interesting. What version of ntp are you using?
> > > >
> > > > Is vesafb one of the drivers which blocks interrupts for (many) tens
> > > > of milliseconds?
> > > 
> > > Vesafb is happy to block interrupts for half a second.
> > 
> > And has this been observed to cause clock drift?
> 
> YEs. I've seen time running 3 times slower. Just do cat /etc/termcap
> with loaded PCI bus. Yesterday I lost 20 minutes during 2 hours -- I
> have been using USB (load PCI) and framebuffer.
> 								Pavel

Is it not possible to save/check TSC in timer interrupt to correct for
dropped interrupts ? (obviously only on machines that have a TSC ...)

P.
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