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Subject: Re: [PATCH] linux-2.5.66_monotonic-clock_A3
From: john stultz <johnstul@us.ibm.com>
To: Andi Kleen <ak@suse.de>
Cc: Linus Torvalds <torvalds@transmeta.com>, Andrew Morton <akpm@digeo.com>,
       lkml <linux-kernel@vger.kernel.org>
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On Fri, 2003-03-28 at 23:57, Andi Kleen wrote:
> john stultz <johnstul@us.ibm.com> writes:
> 
> > +	do {
> > +		seq = read_seqbegin(&xtime_lock);
> > +		ret = timer->monotonic_clock();
> > +	} while (read_seqretry(&xtime_lock, seq));
> 
> Why does it need to check xtime lock ? xtime should be independent 
> of the monotonic time because it can be changed. 

Ok, fair enough. I was using the xtime lock to protect monotonic_base in
(updated in mark_offset()), but since that isn't obvious I should be
more explicit and use a different lock. 

> Also doing seqlocks around hardware register reads is quite nasty,
> because a hardware register read can be hundreds of cycles and you're
> very likely to get retries. If you really need a seqlock I would
> move it into the low level function and do it after the hardware access.
> But as far as I can see it can be just removed.

I should be able to use a regular rwlock w/o troubles. I change that and
resubmit. 

thanks for the feedback!
-john



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