From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754146Ab1I1RM7 (ORCPT ); Wed, 28 Sep 2011 13:12:59 -0400 Received: from claw.goop.org ([74.207.240.146]:38429 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753129Ab1I1RM6 (ORCPT ); Wed, 28 Sep 2011 13:12:58 -0400 Message-ID: <4E835095.5020706@goop.org> Date: Wed, 28 Sep 2011 09:51:33 -0700 From: Jeremy Fitzhardinge 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" , "avi@redhat.com" 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> X-Enigmail-Version: 1.3.2 Content-Type: text/plain; charset=ISO-8859-1 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 05:37 AM, 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? My only interest in the NMI code is its use of spinlocks, which seem inappropriate. J