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Date: Wed, 18 Aug 2010 16:53:03 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: "H. Peter Anvin" <hpa@...or.com> Cc: Alexander Shishkin <virtuoso@...nd.org>, lkml@...r.kernel.org, "Kirill A. Shutemov" <kirill@...temov.name>, Thomas Gleixner <tglx@...utronix.de>, John Stultz <johnstul@...ibm.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, 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>, John Kacur <jkacur@...hat.com>, Chris Friesen <chris.friesen@...band.com>, Kay Sievers <kay.sievers@...y.org>, Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] [RFCv2] notify userspace about time changes On Wed, 18 Aug 2010 16:43:48 -0700 "H. Peter Anvin" <hpa@...or.com> wrote: > On 08/18/2010 03:57 PM, Andrew Morton wrote: > > On Wed, 18 Aug 2010 16:55:39 +0300 > > Alexander Shishkin <virtuoso@...nd.org> wrote: > > > >> Certain userspace applications (like "clock" desktop applets or cron) might > >> want to be notified when some other application changes the system time. > > > > The requirements sound a bit fluffy to me. > > > > Any time-displaying application will find out the new time next time > > it reads the time. So afaict this is only really useful for clock > > applets which display once per minute, so they will show the new time > > promptly after the time was altered, yes? Is that really worth adding > > new code for? > > > > Actually a much more significant use case was given for the "civil > periodic" type events: something that wants to happen "every day at > noon", for example. The logical thing of sleeping until the next noon > breaks if the walltime clock is changed. As such, things like cron have > to resort to wake up once a minute just to assure themselves that they > have nothing to do. This is inefficient, especially for battery-powered > devices. OK. Such applications might be better served via a wake-me-at-this-time syscall instead of a sleep-me-for-this-long syscall. Although such a thing is less general. Is sysfs the right interface for this thing? Bear in mind that CONFIG_SYSFS does exist. > + fd = open("/sys/kernel/time_notify", O_WRONLY); > + fdprintf(fd, "%d 1 0 1 1", efd); why not sys_time_notify(efd, 1, 0, 1, 1); ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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