linux-kernel - Re: [RFC][PATCH] Dynamic Tick: Allow 32-bit machines to sleep for more than 2.15 seconds

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Message-Id: <1240358715.6080.42.camel@localhost>
Date:	Tue, 21 Apr 2009 17:05:15 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Jon Hunter <jon-hunter@...com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] Dynamic Tick: Allow 32-bit machines to sleep for
 more than 2.15 seconds

On Tue, 2009-04-21 at 18:20 -0500, Jon Hunter wrote:
> john stultz wrote:
> > The concern is many clocksources wrap after a handful of seconds. The
> > acpi_pm is the best example (its only 24 bits wide). 
> > 
> > I brought this issue up earlier, and provided some example code that
> > could be used to limit the idle time appropriately for the current
> > clocksource here:
> > 
> > http://lkml.indiana.edu/hypermail/linux/kernel/0901.3/02693.html
> > 
> > Jon: Did you see that mail, or is there a reason you didn't adapt this
> > code into your patch? 
> 
> Hi John, yes I did read this email and thanks for bringing this up.
> 
> As I looked at this more I noticed that for 64-bit machines that the 
> max_delta_ns would be a 64-bit integer already and so this change would 
> only have an impact for 32-bit machines. I understand that there are 
> more 32-bit machines that 64-bit. However, I was trying to understand 
> how the wrapping of clocksources, such as the one you mention above, is 
> handled today for 64-bit machines that could theoretically sleep for 
> longer periods.

One other minor comment nit, if we're really meaning that max_delta_ns
is a 64bit value, should we not just be using s64 and be explicit
instead of converting longs to long longs?

thanks
-john


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