linux-kernel - Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK

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Date:	Wed, 01 Dec 2010 15:46:48 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Valdis.Kletnieks@...edu
Cc:	Jamie Lokier <jamie@...reable.org>,
	Lennart Poettering <mzxreary@...inter.de>,
	Alexander Shishkin <virtuoso@...nd.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Feng Tang <feng.tang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Tokarev <mjt@....msk.ru>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Chris Friesen <chris.friesen@...band.com>,
	Kay Sievers <kay.sievers@...y.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for
 clock changes

On Wed, 2010-12-01 at 17:46 -0500, Valdis.Kletnieks@...edu wrote:
> On Wed, 01 Dec 2010 10:43:59 GMT, Jamie Lokier said:
> 
> > So maybe CLOCK_MONOTONIC should be changed to include elapsed time
> > during suspend/resume, and CLOCK_MONOTONIC_RAW could remain as it is,
> > for programs that want that?
> 
> Wouldn't that be an API break for programs that are expecting the current
> behavior of CLOCK_MONOTONIC?  Yes, there should be a way to request either of
> them - but if there's only one way now, it should continue to act the current
> way, and the added way is the second option.

We do keep track of the amount of time in suspend (total_sleep_time), so
creating a new clockid to provide CLOCK_MONOTONIC + total_sleep_time
wouldn't be hard. We just haven't had a clear articulation of why it
would be useful to expose to userland (nor a clear name to describe
exactly what it represents).

thanks
-john


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