From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965540AbXDBRxA (ORCPT ); Mon, 2 Apr 2007 13:53:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965550AbXDBRw7 (ORCPT ); Mon, 2 Apr 2007 13:52:59 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:49846 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965540AbXDBRw7 (ORCPT ); Mon, 2 Apr 2007 13:52:59 -0400 X-AuthUser: davidel@xmailserver.org Date: Mon, 2 Apr 2007 10:52:56 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Thomas Gleixner cc: Linux Kernel Mailing List , Andrew Morton , Linus Torvalds Subject: Re: [patch 6/13] signal/timer/event fds v9 - timerfd core ... In-Reply-To: <1175536065.28263.177.camel@localhost.localdomain> Message-ID: References: <1175418341.28263.64.camel@localhost.localdomain> <1175498549.28263.88.camel@localhost.localdomain> <1175536065.28263.177.camel@localhost.localdomain> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2 Apr 2007, Thomas Gleixner wrote: > On Mon, 2007-04-02 at 10:30 -0700, Davide Libenzi wrote: > > > > There is no inaccuracy when you rearm the timer on read: hrtimer_forward > > > takes care, that the period is accurate. It does not start the timer out > > > of the periodic order, i.e. on a different time frame. > > > > > > Where is the win of keeping the timer running, when nobody cares about > > > the expiry at all ? It just generates interrupts and events for nothing. > > > > Then you'd lose the ability to know if you lost one or more (yes, you > > could figure it out by reading the time and with a few calculations). I > > think that the capping (to a sane value) idea solves the DoS issue and at > > the same time have the ability to report you missed ticks. What are your > > strong points against that solution? > > Err, the read function > > ticks = hrtimer_forward(&ctx->tmr, ktime_get(), > ctx->tintv); > > does give you the number of (lost) ticks. > > tmr->expires holds the absolute expiry time of the last event. > hrtimer_forward() adds N intervals to tmr->expires, so that the new > tmr->expires value is greater than now (ktime_get()). It returns N. > > So the number of lost ticks is N - 1. No time reading and no magic > math :) Yack, I missed that part :) Sounds fine then. - Davide