From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754266Ab2BCAbH (ORCPT ); Thu, 2 Feb 2012 19:31:07 -0500 Received: from e7.ny.us.ibm.com ([32.97.182.137]:38665 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753190Ab2BCAbE (ORCPT ); Thu, 2 Feb 2012 19:31:04 -0500 Date: Thu, 2 Feb 2012 16:29:02 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Mikulas Patocka , axboe@kernel.dk, "Alasdair G. Kergon" , dm-devel@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] backing-dev: use synchronize_rcu_expedited instead of synchronize_rcu Message-ID: <20120203002902.GQ2518@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1328042063.2446.250.camel@twins> <1328219944.2446.277.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1328219944.2446.277.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12020300-5806-0000-0000-00001200CE68 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 02, 2012 at 10:59:04PM +0100, Peter Zijlstra wrote: > On Thu, 2012-02-02 at 15:43 -0500, Mikulas Patocka wrote: > > Do you have some measurable use case where the user is removing block > > devices so heavily that this causes a problem? > > Even one can be a problem, we're having people spend lots of time and > effort to reduce machine wide jitter and interference. Adding it with > such disregard isn't cool. > > There's no reason a management cpu adding or removing block devices > should perturb the high-freq trading or industrial laser control running > on the other side of the machine. Very true for real-time applications! For the heavy trading apps, given Frederic's upcoming user-mode-idle work, I can keep this stuff from perturbing the apps. Still, batching would be preferable. Thanx, Paul