From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754392Ab2AaNuR (ORCPT ); Tue, 31 Jan 2012 08:50:17 -0500 Received: from casper.infradead.org ([85.118.1.10]:51914 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753237Ab2AaNuQ convert rfc822-to-8bit (ORCPT ); Tue, 31 Jan 2012 08:50:16 -0500 Message-ID: <1328017807.2446.230.camel@twins> Subject: Re: [RFC][PATCH] srcu: Implement call_srcu() From: Peter Zijlstra To: Avi Kivity Cc: "Paul E. McKenney" , Oleg Nesterov , linux-kernel , Marcelo Tosatti , KVM list Date: Tue, 31 Jan 2012 14:50:07 +0100 In-Reply-To: <4F27F0E6.1040309@redhat.com> References: <1328016724.2446.229.camel@twins> <4F27F0E6.1040309@redhat.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.1- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ;-)