From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756500Ab2IZNjY (ORCPT ); Wed, 26 Sep 2012 09:39:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34854 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493Ab2IZNjX (ORCPT ); Wed, 26 Sep 2012 09:39:23 -0400 Date: Wed, 26 Sep 2012 15:39:05 +0200 From: Andrew Jones To: Peter Zijlstra Cc: Avi Kivity , Raghavendra K T , "H. Peter Anvin" , Marcelo Tosatti , Ingo Molnar , Rik van Riel , Srikar , "Nikunj A. Dadhania" , KVM , Jiannan Ouyang , chegu vinod , "Andrew M. Theurer" , LKML , Srivatsa Vaddagiri , Gleb Natapov Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler Message-ID: <20120926133905.GA8842@turtle.usersys.redhat.com> References: <1348486479.11847.46.camel@twins> <50604988.2030506@linux.vnet.ibm.com> <1348490165.11847.58.camel@twins> <50606050.309@linux.vnet.ibm.com> <1348494895.11847.64.camel@twins> <50608176.1040805@redhat.com> <1348502600.11847.90.camel@twins> <5060883C.4050901@redhat.com> <20120926132013.GB7633@turtle.usersys.redhat.com> <1348665971.3881.102.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1348665971.3881.102.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 26, 2012 at 03:26:11PM +0200, Peter Zijlstra wrote: > On Wed, 2012-09-26 at 15:20 +0200, Andrew Jones wrote: > > Wouldn't a clean solution be to promote a task's scheduler > > class to the spinner class when we PLE (or come from some special > > syscall > > for userspace spinlocks?)? > > Userspace spinlocks are typically employed to avoid syscalls.. I'm guessing there could be a slow path - spin N times and then give up and yield. > > > That class would be higher priority than the > > fair class and would schedule in FIFO order, but it would only run its > > tasks for short periods before switching. > > Since lock hold times aren't limited, esp. for things like userspace > 'spin' locks, you've got a very good denial of service / opportunity for > abuse right there. Maybe add some throttling to avoid overuse/maliciousness? > > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html