From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 10 Sep 2001 14:52:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 10 Sep 2001 14:52:42 -0400 Received: from ns.caldera.de ([212.34.180.1]:13289 "EHLO ns.caldera.de") by vger.kernel.org with ESMTP id ; Mon, 10 Sep 2001 14:52:34 -0400 Date: Mon, 10 Sep 2001 20:52:50 +0200 From: Christoph Hellwig To: Andrea Arcangeli Cc: linux-kernel@vger.kernel.org Subject: Re: 2.4.10pre7aa1 Message-ID: <20010910205250.B22889@caldera.de> Mail-Followup-To: Christoph Hellwig , Andrea Arcangeli , linux-kernel@vger.kernel.org In-Reply-To: <20010910175416.A714@athlon.random> <200109101741.f8AHfwx17136@ns.caldera.de> <20010910200344.C714@athlon.random> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20010910200344.C714@athlon.random>; from andrea@suse.de on Mon, Sep 10, 2001 at 08:03:44PM +0200 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 10, 2001 at 08:03:44PM +0200, Andrea Arcangeli wrote: > > Do we really need yet-another per-CPU thread for this? I'd prefer to have > > the context thread per-CPU instead (like in Ben's asynchio patch) and do > > this as well. > > The first desing solution I proposed to Paul and Dipankar was just to > use ksoftirqd for that (in short set need_resched and wait it to be > cleared), it worked out nicely and it was a sensible improvement with > respect to their previous patches. (also it was reliable, we cannot > afford allocations in the wait_for_rcu path to avoid having to introduce > fail paths) it was also a noop to the ksoftirqd paths. > > However they remarked ksoftirqd wasn't a RT thread so under very high > load it could introduce an higher latency to the wait_for_rcu calls. Hmm, I don't see why latency is important for rcu - we only want to free datastructures.. (mm load?). On the other hands they are the experts on RCU, not I so I'll believe them. > So in short if you really are in pain for 8k per cpu to get the best > runtime behaviour and cleaner code I'd at least suggest to use the > ksoftirqd way that should be the next best step. My problem with this appropech is just that we use kernel threads for more and more stuff - always creating new ones. I think at some point they will sum up badly. Christoph -- Of course it doesn't work. We've performed a software upgrade.