From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] backing-dev: use synchronize_rcu_expedited instead of synchronize_rcu Date: Thu, 2 Feb 2012 16:29:02 -0800 Message-ID: <20120203002902.GQ2518@linux.vnet.ibm.com> References: <1328042063.2446.250.camel@twins> <1328219944.2446.277.camel@twins> Reply-To: paulmck@linux.vnet.ibm.com, device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1328219944.2446.277.camel@twins> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Peter Zijlstra Cc: axboe@kernel.dk, dm-devel@redhat.com, Mikulas Patocka , linux-kernel@vger.kernel.org, "Alasdair G. Kergon" List-Id: dm-devel.ids 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