From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755440Ab2AaWYx (ORCPT ); Tue, 31 Jan 2012 17:24:53 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:41550 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753461Ab2AaWYw (ORCPT ); Tue, 31 Jan 2012 17:24:52 -0500 Date: Tue, 31 Jan 2012 14:24:47 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Avi Kivity , Oleg Nesterov , linux-kernel , Marcelo Tosatti , KVM list Subject: Re: [RFC][PATCH] srcu: Implement call_srcu() Message-ID: <20120131222447.GH2391@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1328016724.2446.229.camel@twins> <4F27F0E6.1040309@redhat.com> <1328017807.2446.230.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1328017807.2446.230.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12013122-5518-0000-0000-000001EABC8C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 31, 2012 at 02:50:07PM +0100, Peter Zijlstra wrote: > On Tue, 2012-01-31 at 15:47 +0200, Avi Kivity wrote: > > > They really need to return quickly to userspace, and they really need to > > perform some operation between rcu_assign_pointer() and returning, so no. > > Bugger :/ > > > > > > > Compile tested only!! :-) > > > > > > > How much did synchronize_srcu_expedited() regress? Presumably your > > compiler didn't tell you that. > > Nope, quite a lot I figure. > > > Can we get it back to speed by scheduling a work function on all cpus? > > wouldn't that force a quiescent state and allow call_srcu() to fire? > > > > In kvm's use case synchronize_srcu_expedited() is usually called when no > > thread is in a critical section, so we don't have to wait for anything > > except the srcu machinery. > > OK, I'll try and come up with means of making it go fast again ;-) I cannot resist suggesting a kthread to do the call_srcu(), which would allow synchronize_srcu_expedited() to proceed with its current brute-force speed. Thanx, Paul