Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262535AbUCWMtz (ORCPT ); Tue, 23 Mar 2004 07:49:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262538AbUCWMtz (ORCPT ); Tue, 23 Mar 2004 07:49:55 -0500 Received: from ppp-217-133-42-200.cust-adsl.tiscali.it ([217.133.42.200]:25037 "EHLO dualathlon.random") by vger.kernel.org with ESMTP id S262535AbUCWMtw (ORCPT ); Tue, 23 Mar 2004 07:49:52 -0500 Date: Tue, 23 Mar 2004 13:50:44 +0100 From: Andrea Arcangeli To: Dipankar Sarma Cc: Arjan van de Ven , tiwai@suse.de, Robert Love , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH] RCU for low latency (experimental) Message-ID: <20040323125044.GL22639@dualathlon.random> References: <20040323101755.GC3676@in.ibm.com> <1080038105.5296.8.camel@laptop.fenrus.com> <20040323123105.GI22639@dualathlon.random> <20040323124002.GH3676@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040323124002.GH3676@in.ibm.com> User-Agent: Mutt/1.4.1i X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1674 Lines: 36 On Tue, Mar 23, 2004 at 06:10:02PM +0530, Dipankar Sarma wrote: > On Tue, Mar 23, 2004 at 01:31:05PM +0100, Andrea Arcangeli wrote: > > On Tue, Mar 23, 2004 at 11:35:06AM +0100, Arjan van de Ven wrote: > > > > > > > Reduce bh processing time of rcu callbacks by using tunable per-cpu > > > > krcud daemeons. > > > > > > why not just use work queues ? > > > > I don't know if work queues are scheduler friendly, but definitely the > > rearming tasklets are. Running a dozen callbacks per pass and queueing > > any remining work to a rearming tasklet should fix it. > > One problem that likely happen here is that under heavy interrupt > load, large number of softirqs still starve out user processes. Disagree, run 1 callback per tasklet and then you will not measure the cost of this callback compared to the cost of talking to the hardware entering/exiting kernel etc... > In my DoS testing setup, I see that limiting RCU softirqs > and re-arming tasklets has no effect on user process starvation. in an irq flood load that stalls userspace anyways it's ok to spread the callback load into the irqs, 10 tasklets and in turn 10 callbacks per irqs or so. That load isn't scheduler friendly anyways. the one property you need is not to be RT like eventd, to be scheduler friendly, but guaranteed to make progress too and that's what softirqs can give you and that's why I used only softirqs in my rcu_poll patches too ;). - 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/