Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754957Ab0KKKc3 (ORCPT ); Thu, 11 Nov 2010 05:32:29 -0500 Received: from eu1sys200aog107.obsmtp.com ([207.126.144.123]:58607 "EHLO eu1sys200aog107.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753242Ab0KKKc1 (ORCPT ); Thu, 11 Nov 2010 05:32:27 -0500 Message-ID: <4CDBC60F.8070905@stericsson.com> Date: Thu, 11 Nov 2010 11:31:43 +0100 From: Linus Walleij User-Agent: Thunderbird 2.0.0.24 (X11/20100411) MIME-Version: 1.0 To: Thomas Gleixner 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 References: <1289466356-16697-1-git-send-email-linus.walleij@stericsson.com> In-Reply-To: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 30 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. > Aside of that you are trading a bit less source code with extra code > in the clock read() function, which is called pretty frequently. Hm, yeah. I would have to go to metrics but it's O(n) is it not? Shouldn't hurt a high-frequency SMP system I believe. Yours, Linus Walleij -- 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/