From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752573AbaESB5T (ORCPT ); Sun, 18 May 2014 21:57:19 -0400 Received: from mail-pa0-f52.google.com ([209.85.220.52]:34588 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752500AbaESB5R (ORCPT ); Sun, 18 May 2014 21:57:17 -0400 Message-ID: <1400464540.9630.31.camel@debian> Subject: Re: [PATCH] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU From: Chen Yucong To: Borislav Petkov Cc: tony.luck@intel.com, linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org Date: Mon, 19 May 2014 09:55:40 +0800 In-Reply-To: <20140518163508.GA8003@pd.tnic> References: <1400425504-8821-1-git-send-email-slaoub@gmail.com> <20140518163508.GA8003@pd.tnic> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2014-05-18 at 18:35 +0200, Borislav Petkov wrote: > On Sun, May 18, 2014 at 11:05:04PM +0800, Chen Yucong wrote:a > > mces_seen is a Per-CPU variable which should only be accessed by > > Per-CPU as possible. So the clear operation of mces_seen should also > > be lcoal to Per-CPU rather than monarch CPU. > > No, you need to do the cleaning in mce_reign because the monarch cpu has > to run last after all other cpus have scanned their mce banks. > But all other CPUs also have to wait monarch CPU to exit from mce_end. What's the difference between monarch CPU and Per-CPU for clearing mces_seen? In practice, there is no difference between them. If we use monarch CPU to clear mces_seen, then Per-CPU variable can not play out its advantage. > > Meanwhile, there is also a potential risk that mces_seen will not > > be be cleared if a timeout occors in mce_end for monarch CPU. As a > > reuslt, the stale value of mces_seen will reappear on the next mce. > > If that happens, we have a bigger problem. Well, in that case, why is there a need for time-out machine in MCE handler? Any potential risks --both logical and realistic-- should be avoided as possible if there are no more questions and performance penalty. thx! cyc > > Is that a real issue you're trying to address?