linux-kernel - Re: [PATCH] [RFC] notify userspace about time changes

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Date:	Thu, 5 Aug 2010 15:39:28 +0300
From:	Alexander Shishkin <virtuoso@...nd.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Chris Friesen <chris.friesen@...band.com>, gregkh@...e.de,
	lkml@...r.kernel.org, "Kirill A. Shutemov" <kirill@...temov.name>,
	Thomas Gleixner <tglx@...utronix.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jon Hunter <jon-hunter@...com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Avi Kivity <avi@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	John Kacur <jkacur@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] notify userspace about time changes

On 5 August 2010 03:52, john stultz <johnstul@...ibm.com> wrote:
> On Wed, 2010-08-04 at 12:48 -0600, Chris Friesen wrote:
>> On 08/04/2010 09:58 AM, john stultz wrote:
>>
>> > Is there a actual use case that you need this for?  I don't really have
>> > an issue with the code I just really want to make sure the feature would
>> > be useful enough to justify the API and code maintenance going forward.
>>
>> We actually added a time-change-notification mechanism internally a long
>> time ago but never saw demand for it and so never bothered trying to
>> push it upstream.  Ours is signal-based.
>>
>> Among other things we use it to pass on time-change notifications to an
>> emulator running a proprietary OS that really cares about having an
>> accurate time-of-day but can't afford a syscall to retrieve it every time.
>
> So the eventfd based method (and the filtering) proposed would work for
> you?

I think that Kirill has a point and the filtering is really there for
no gain. The user
can indeed count his own time changes and compare that against the eventfd
counter.

Regards,
--
Alex
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