From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dipankar Sarma Subject: Re: Question about usage of RCU in the input layer Date: Thu, 19 Mar 2009 14:26:28 +0530 Message-ID: <20090319085628.GA6167@in.ibm.com> References: <20090318215812.15496a86@infradead.org> Reply-To: dipankar@in.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e1.ny.us.ibm.com ([32.97.182.141]:42284 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754390AbZCSI4g (ORCPT ); Thu, 19 Mar 2009 04:56:36 -0400 Content-Disposition: inline In-Reply-To: <20090318215812.15496a86@infradead.org> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Arjan van de Ven Cc: linux-input@vger.kernel.org, dmitry.torokhov@gmail.com, linux-kernel@vger.kernel.org On Wed, Mar 18, 2009 at 09:58:12PM -0700, Arjan van de Ven wrote: > Hi, > > the input layer does a "synchronize_rcu()" after a list_add_tail_rcu(), which > is costing me 1 second of boot time..... > And based on my understanding of the RCU concept, you only need to synchronize on delete, > not on addition... so I think the synchronize is entirely redundant here... > The more appropriate question is - why is synchronize_rcu() taking 1 second ? Any idea what the other CPUs are doing at the time of calling synchronize_rcu() ? What driver is this ? How early in the boot is this happening ? Thanks Dipankar