From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752211Ab1JBKIG (ORCPT ); Sun, 2 Oct 2011 06:08:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1026 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752204Ab1JBKH5 (ORCPT ); Sun, 2 Oct 2011 06:07:57 -0400 Message-ID: <4E8837D4.5040607@redhat.com> Date: Sun, 02 Oct 2011 12:07:16 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2 MIME-Version: 1.0 To: Don Zickus CC: Robert Richter , "x86@kernel.org" , Andi Kleen , Peter Zijlstra , "ying.huang@intel.com" , LKML , "paulmck@linux.vnet.ibm.com" , "jeremy@goop.org" Subject: Re: [V6][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs References: <1316805435-14832-1-git-send-email-dzickus@redhat.com> <1316805435-14832-5-git-send-email-dzickus@redhat.com> <20110928103140.GD6063@erda.amd.com> <20110928123720.GL5795@redhat.com> In-Reply-To: <20110928123720.GL5795@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/28/2011 03:37 PM, Don Zickus wrote: > On Wed, Sep 28, 2011 at 12:31:40PM +0200, Robert Richter wrote: > > On 23.09.11 15:17:13, Don Zickus wrote: > > > @@ -89,6 +89,15 @@ static int notrace __kprobes nmi_handle(unsigned int type, struct pt_regs *regs) > > > > > > handled += a->handler(type, regs); > > > > > > + /* > > > + * Optimization: only loop once if this is not a > > > + * back-to-back NMI. The idea is nothing is dropped > > > + * on the first NMI, only on the second of a back-to-back > > > + * NMI. No need to waste cycles going through all the > > > + * handlers. > > > + */ > > > + if (!b2b&& handled) > > > + break; > > > > I don't think we can leave this in. As said, there are cases that 2 > > nmis trigger but the handler is called only once. Only the first would > > be handled then, and the second get lost cause there is no 2nd nmi > > call. > > Right. Avi, Jeremy what was your objection that needed this optimization > in the first place? > First, iterating over all NMI sources is going to be slow, and a lot more so in a guest. This reduces the performance of perf. Second, I wanted to use NMIs as a way of waking up a vcpu sleeping with interrupts disabled (in the context of Jeremy's paravirt spinlock patches). Looks like we'll have to use paravirtualization for that. -- error compiling committee.c: too many arguments to function