Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755819Ab0LBB4M (ORCPT ); Wed, 1 Dec 2010 20:56:12 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:48777 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753502Ab0LBB4K (ORCPT ); Wed, 1 Dec 2010 20:56:10 -0500 Subject: Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes From: john stultz To: Jamie Lokier 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 In-Reply-To: <20101202011832.GO22787@shareable.org> 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> Content-Type: text/plain; charset="UTF-8" Date: Wed, 01 Dec 2010 17:55:57 -0800 Message-ID: <1291254957.2846.47.camel@work-vm> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2058 Lines: 48 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. > Currently CLOCK_MONOTONIC jumps forwards by 4 seconds on > suspend/resume anyway (as seen by userspace), on my x86 laptop running > 2.6.37-rc3. So it does already jump a bit... So just to clarify here, by this do you mean that there's ~4 seconds delay between the resume event and when userland apps start to run (or possibly some of that accumulating between the app freeze and the timekeeping suspend) ? Or are you seeing CLOCK_MONOTONIC jump 4 seconds out of sync with CLOCK_REALTIME? It should be the delta between CLOCK_MONOTONIC and CLOCK_REALTIME prior to suspend should be that same delta + suspend time after resume. If that's not the case, something may be broken. thanks -john -- 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/