Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753671Ab1CKT5z (ORCPT ); Fri, 11 Mar 2011 14:57:55 -0500 Received: from www.tglx.de ([62.245.132.106]:33189 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751677Ab1CKT5x (ORCPT ); Fri, 11 Mar 2011 14:57:53 -0500 Date: Fri, 11 Mar 2011 20:56:49 +0100 (CET) From: Thomas Gleixner To: Scott James Remnant cc: Andrew Morton , Alexander Shishkin , linux-kernel@vger.kernel.org, Ken MacLeod , Shaun Reich , Alexander Viro , Greg Kroah-Hartman , Feng Tang , Michael Tokarev , Marcelo Tosatti , John Stultz , Chris Friesen , Kay Sievers , "Kirill A. Shutemov" , Artem Bityutskiy , Davide Libenzi , linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Michael Kerrisk Subject: Re: [RFCv4] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes In-Reply-To: Message-ID: References: <1299681411-9227-1-git-send-email-virtuoso@slind.org> <20110309162513.5058c824.akpm@linux-foundation.org> <20110310002534.f984f8b2.akpm@linux-foundation.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="-1463795968-244858380-1299873414=:2787" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2527 Lines: 59 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463795968-244858380-1299873414=:2787 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT On Fri, 11 Mar 2011, Scott James Remnant wrote: > On Thu, Mar 10, 2011 at 12:25 AM, Andrew Morton > wrote: > > On Wed, 9 Mar 2011 18:01:09 -0800 Scott James Remnant wrote: > > > >> > It would be helpful to know if the identified users of this feature > >> > actually find it useful and adequate. __I guess the most common > >> > application is the 1,001 desktop clock widgets. __Do you have any > >> > feedback from any of the owners of those? > >> > > >> cron is another obvious one (or init systems attempting to replace > >> cron). Having to wakeup and check the time every minute can be > >> non-conducive to power savings, it would be better if we could just > >> sleep until the next alarm and be woken up if the time changes in > >> between. > >> > >> (That being said, we also need to poll for and/or check for timezone > >> changes - but those are entirely userspace, so we can deal with that > >> separately) > > > > Sure, there will be lots of applications. > > > > But what I'm asking isn't "it is a good feature". ?I'm asking "is the > > feature implemented well". ?Ideally someone would get down and modify > > cron to use the interface in this patch. > > > So I've just been thinking today - and I'm actually not sure whether > this is needed at all for this case. > > A good cron implementation is going to set timers according to > CLOCK_REALTIME; in the case where the clock changes forwards, those > timers will fire as part of the clock changing already no? And in the > case where the clock changes backwards, you don't want to re-run old > ones anyway. > > Even the hourly/daily cases are actually at a fixed time, so would be > triggered - and a decent implementation wouldn't trigger a given > script more than once. Yeah, I was wondering about today as well. Though when you set back your clock several days, stuff might be surprised if it's not woken up for several days :) Thanks, tglx ---1463795968-244858380-1299873414=:2787-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/