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

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Date:	Thu, 01 Feb 2007 08:56:48 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.cz>, 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, 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.

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

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