Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755814Ab0KKLFU (ORCPT ); Thu, 11 Nov 2010 06:05:20 -0500 Received: from www.tglx.de ([62.245.132.106]:42315 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755703Ab0KKLFQ (ORCPT ); Thu, 11 Nov 2010 06:05:16 -0500 Date: Thu, 11 Nov 2010 12:05:03 +0100 (CET) From: Thomas Gleixner To: Linus Walleij cc: "linux-kernel@vger.kernel.org" , Nicolas Pitre , "linux-arm-kernel@lists.infradead.org" , Colin Cross , Rabin VINCENT Subject: Re: [PATCH] RFC: nomadik: expand timesource to 63 bits In-Reply-To: <4CDBC60F.8070905@stericsson.com> Message-ID: References: <1289466356-16697-1-git-send-email-linus.walleij@stericsson.com> <4CDBC60F.8070905@stericsson.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1214 Lines: 30 On Thu, 11 Nov 2010, Linus Walleij wrote: > Thomas Gleixner wrote: > > > There is only one caveat. When nohz is on and you sleep longer than 16 > > seconds then the limitation we have in place does not work anymore, as > > it would say that the long sleep time is less than the 63bit > > wraparound time. With 32bit clocksource it limits the sleep correclty > > to avoid the clocksource wrap issue. > > Hm! So the .mask has that side effect (as I suspected), and with > this the sleep will be limited to what time you can get into 63 bits > (2200 years). And we sure want NOHZ... > > But if I complement the solution with the keepwarm() timer from > Orion doing just a dummy read() on the clocksource every say 15 secs > it will work even if the system sleeps for so long. Well, you don't need the keepwarm() timer, if you just call sched_clock() in the idle wakeup path, so the magic in the NOHZ code will ensure that you reread the thing timely. Thanks, tglx -- 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/