From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261204AbULJUiD (ORCPT ); Fri, 10 Dec 2004 15:38:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261200AbULJUiC (ORCPT ); Fri, 10 Dec 2004 15:38:02 -0500 Received: from e33.co.us.ibm.com ([32.97.110.131]:28388 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S261826AbULJUhp (ORCPT ); Fri, 10 Dec 2004 15:37:45 -0500 Date: Sat, 11 Dec 2004 02:10:03 +0530 From: Dipankar Sarma To: George Anzinger Cc: ganzinger@mvista.com, Manfred Spraul , lkml Subject: Re: RCU question Message-ID: <20041210204003.GC4073@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <41B8E6F1.4070007@mvista.com> <20041210043102.GC4161@in.ibm.com> <41B9FC3F.50601@mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41B9FC3F.50601@mvista.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 10, 2004 at 11:42:55AM -0800, George Anzinger wrote: > Dipankar Sarma wrote: > >And yes, RCU processing in softirq context can re-raise the softirq. > >AFAICS, it is perfectly normal. > > My assumption was that, this being the idle task, RCU would be more than > happy to finish all its pending tasks. We try to avoid really long running softirqs (RCU tasklet in this case) for better scheduling latency. A long running rcu tasklet during an idle cpu may delay running of an RT process that becomes runnable during the rcu tasklet. > > It may be necessary for me to rethink the conditions required to go into > the VST state. I had assumed that it required NO softirq pending as a pre > condition. From this point on we would have the interrupt system off until > the hardware sleep instruction (hlt in the x86 case). Unfortunately, we aren't there yet. But it is in my TODO list for a generic nohz system. Thanks Dipankar