From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 1/3] sfq: timer is deferrable Date: Fri, 18 Jan 2008 21:57:00 -0800 Message-ID: <20080119055700.GC24840@linux.vnet.ibm.com> References: <20080118144900.1df0dd90@deepthought> <20080119043446.GB24840@linux.vnet.ibm.com> <20080118203655.3b6fbfc9@deepthought> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Stephen Hemminger , David Miller , netdev@vger.kernel.org To: Stephen Hemminger Return-path: Received: from e31.co.us.ibm.com ([32.97.110.149]:52238 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751684AbYASF5M (ORCPT ); Sat, 19 Jan 2008 00:57:12 -0500 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e31.co.us.ibm.com (8.13.8/8.13.8) with ESMTP id m0J5v7jd031521 for ; Sat, 19 Jan 2008 00:57:07 -0500 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m0J5v2Pd111456 for ; Fri, 18 Jan 2008 22:57:07 -0700 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m0J5v12d003183 for ; Fri, 18 Jan 2008 22:57:01 -0700 Content-Disposition: inline In-Reply-To: <20080118203655.3b6fbfc9@deepthought> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, Jan 18, 2008 at 08:36:55PM -0800, Stephen Hemminger wrote: > On Fri, 18 Jan 2008 20:34:46 -0800 > "Paul E. McKenney" wrote: > > > On Fri, Jan 18, 2008 at 02:49:00PM -0800, Stephen Hemminger wrote: > > > The perturbation timer used for re-keying can be deferred, it doesn't > > > need to be deterministic. > > > > The only concern that I can come up with is that the sfq_perturbation > > timer might be on one CPU, and all the operations using the corresponding > > SFQ on another. This could in theory allow a nearly omniscient attacker > > to exploit an SFQ imbalance while preventing perturbation of the hash > > function. > > > > This does not seem to be a valid concern at this point, since there are > > very few uses of init_timer_deferrable(). And if it should become a > > problem, one approach would be to have some sort of per-timer limit to > > the deferral. Of course, at that point one would need to figure out > > what this limit should be! > > > > Acked-by: Paul E. McKenney > > But the only threat is getting more bandwidth for a longer interval. > It is all kind of moot anyway because the bandwidth hogs all open > multiple connections anyway, so SFQ is of no use. Good point, and an additional reason for my Acked-by above. ;-) Thanx, Paul