linux-kernel - Re: [patch 0/9] x86_64: reliable TSC-based gettimeofday

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Message-ID: <20070201194109.GA21971@suse.cz>
Date:	Thu, 1 Feb 2007 20:41:09 +0100
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	john stultz <johnstul@...ibm.com>
Cc:	Jiri Bohac <jbohac@...e.cz>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, ssouhlal@...ebsd.org,
	arjan@...radead.org, tglx@...utronix.de, zippel@...ux-m68k.org,
	andrea@...e.de
Subject: Re: [patch 0/9] x86_64: reliable TSC-based gettimeofday

On Thu, Feb 01, 2007 at 08:56:48AM -0800, john stultz wrote:
> On Thu, 2007-02-01 at 15:52 +0100, Jiri Bohac wrote:
> > On Thu, Feb 01, 2007 at 12:20:59PM +0100, Andi Kleen wrote:
> >>
> > > The big strategic problem is how to marry your patchkit to John Stultz's
> > > clocksources work which is also competing for merge. Any thoughts on that? 
> > 
> > I'll look into that next week. Sorry, I wanted to do that a long time
> > ago, but I spent weeks (over a month) fighting a nasty livelock
> > in the code. (Morale: think twice before using a spinlock inside
> >                       a {do .. while (read_seqretry(..))} loop)
> 
> The first step here shouldn't be too difficult. Just create a _read
> function that uses your code to return monotonic TSC cycles (instead of
> nanoseconds w/ gettimeofday).  Then just create a clocksource structure
> for it.

guess_mt() is more or less the function you're looking for. (With the
exception of the cpufreq and mode switching logic.)

> The harder part will be the vsyscall, as you will need extra per cpu
> data in the vsyscall read. I had some test code for this situation
> awhile back, so if you get the first part functioning correctly (just a
> clocksource w/o a vread pointer), I'll gladly help you get the vsyscall
> bits working.
> 
> thanks
> -john
> 
> 

-- 
Vojtech Pavlik
Director SuSE Labs
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