From mboxrd@z Thu Jan 1 00:00:00 1970 From: john stultz Subject: Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes Date: Fri, 03 Dec 2010 16:57:52 -0800 Message-ID: <1291424272.15266.8.camel@work-vm> References: <1290532938-7332-1-git-send-email-virtuoso@slind.org> <20101123224346.GA19350@tango.0pointer.de> <20101201104359.GJ22787@shareable.org> <20180.1291243569@localhost> <20101202011832.GO22787@shareable.org> <1291254957.2846.47.camel@work-vm> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Valdis.Kletnieks@vt.edu, Lennart Poettering , Alexander Shishkin , linux-kernel@vger.kernel.org, Thomas Gleixner , Alexander Viro , Greg Kroah-Hartman , Feng Tang , Andrew Morton , Michael Tokarev , Marcelo Tosatti , Chris Friesen , Kay Sievers , "Kirill A. Shutemov" , Artem Bityutskiy , Davide Libenzi , linux-fsdevel@vger.kernel.org To: Jamie Lokier Return-path: In-Reply-To: <1291254957.2846.47.camel@work-vm> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2010-12-01 at 17:55 -0800, john stultz wrote: > On Thu, 2010-12-02 at 01:18 +0000, Jamie Lokier wrote: > > Valdis.Kletnieks@vt.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. > > > > I don't know. Can you think of any program which would break if > > suspend/resume's clocks behaved like ordinary task scheduling - when a > > task doesn't run for a long time because of scheduling decisions? > > Hmm, I guess some realtime apps might like to know. > > Like I mentioned earlier, CLOCK_MONOTONIC_RAW and CLOCK_MONOTONIC are > tightly tied, so anything using CLOCK_MONOTONIC_RAW would break. > > It might be possible to change both, but I still think such a change > would be bad. So actually, as I think more about this, I'm starting to come around to the side that maybe CLOCK_MONOTONIC should be changed to increment during suspend (CLOCK_MONOTONIC_RAW could also be moved forward by the same amount, which isn't really ideal, but maybe not problematic). There are still quite a number of problems that might be caused by such a change. So it may still be impractical to actually do, but more and more it does seem like it might be the better approach. I keep thinking about it. thanks -john