From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751567AbaEUDVh (ORCPT ); Tue, 20 May 2014 23:21:37 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:56939 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751067AbaEUDVf (ORCPT ); Tue, 20 May 2014 23:21:35 -0400 Message-ID: <1400642398.14703.42.camel@debian> Subject: Re: [PATCH v2] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU From: Chen Yucong To: Hidetoshi Seto Cc: tony.luck@intel.com, bp@alien8.de, ak@linux.intel.com, ying.huang@intel.com, linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org Date: Wed, 21 May 2014 11:19:58 +0800 In-Reply-To: <537C12BC.6080408@jp.fujitsu.com> References: <1400551885-13828-1-git-send-email-slaoub@gmail.com> <537C040E.3040901@jp.fujitsu.com> <1400637782.14703.32.camel@debian> <537C12BC.6080408@jp.fujitsu.com> 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 Wed, 2014-05-21 at 11:43 +0900, Hidetoshi Seto wrote: > (2014/05/21 11:03), Chen Yucong wrote: > > On Wed, 2014-05-21 at 10:40 +0900, Hidetoshi Seto wrote: > >> (2014/05/20 11:11), Chen Yucong wrote: > >>> 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. > >> > >> I don't think it should be local. > >> Originally what we want to have here is memory to save mces_seen for each online cpus, > >> such as a global array like mces_seen[cpus]. But at same time we don't want to preallocate > >> big array enough for max possible cpus. So we use per-cpu store instead. > >> > > But mces_seen will just be updated by Per-CPU rather than monarch CPU. > > It is only read by monarch CPU. > > Because mce status registers are per-cpu and monarch cannot access subjects' registers > directly, Right. This is one reason why we need to distribute the clear operation to Per-CPU. And in fact it exactly assigns per-cpu property to mces_seen. > all subjects read it's status for monarch, store the status to memory for monarch, > and then monarch gather all status to make decision for all. mce_regin, which is only called by monarch CPU, can be used for system panics as quickly as possible if there is a truly data corrupting error. But Monarch CPU don't have to help all other CPU to clean mces_clean. One advantage of Per-CPU is the isolation of errors propagation, being so, why do not we clean mces_seen by Per-CPU? thx! cyc > > At last monarch kindly clear gathered status for all. > It will be one of important steps to ready for next mce events. > > I think you should clarify why "distributing the clear operation" is required here. > What is the benefit? >