From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH 0/8] use jump labels to streamline common APIC configuration Date: Tue, 14 Aug 2012 17:08:06 +0300 Message-ID: <20120814140805.GO11194@redhat.com> References: <1344171513-4659-1-git-send-email-gleb@redhat.com> <501E760E.9050109@redhat.com> <20120805133549.GL27579@redhat.com> <501E7839.2030008@redhat.com> <20120805134842.GM27579@redhat.com> <501E7C85.70001@redhat.com> <20120805140305.GN27579@redhat.com> <502A5A16.6040506@siemens.com> <502A5AE0.3080608@redhat.com> <502A5B42.2040102@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , "kvm@vger.kernel.org" , "mtosatti@redhat.com" To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:55848 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752730Ab2HNOII (ORCPT ); Tue, 14 Aug 2012 10:08:08 -0400 Content-Disposition: inline In-Reply-To: <502A5B42.2040102@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Aug 14, 2012 at 04:05:54PM +0200, Jan Kiszka wrote: > On 2012-08-14 16:04, Avi Kivity wrote: > > On 08/14/2012 05:00 PM, Jan Kiszka wrote: > > > >>>> The host can prevent this by leaving disabling the guest pmu. But > >>>> disabling jump labels for real-time kernels may be acceptable too. We > >>>> can probably to it at run time by forcing the slow path at all times. > >>> Yes, it is possible to add module option that will force slow path if > >>> needed. > >> > >> Should I write a patch or will you? Having host-side stop_machine due to > >> such common guest operations is indeed a no-go for RT. > >> > > > > Note that an additional patch is needed for perf, otherwise the guest > > (or a user, but that's less of a concern for realtime) can easily invoke > > stop_machine by configuring and unconfiguring its pmu. > > Hmm, can't the PMU be blocked by taking away some CPU features? > It can. -- Gleb.