From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751672AbeDFImT (ORCPT ); Fri, 6 Apr 2018 04:42:19 -0400 Received: from mail.cn.fujitsu.com ([183.91.158.132]:32579 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751312AbeDFImR (ORCPT ); Fri, 6 Apr 2018 04:42:17 -0400 X-IronPort-AV: E=Sophos;i="5.43,368,1503331200"; d="scan'208";a="38644329" Subject: Re: [PATCH] genirq: only scan the present CPUs To: Peter Zijlstra , Thomas Gleixner CC: Li RongQing , LKML References: <1522647902-11426-1-git-send-email-lirongqing@baidu.com> <20180403112311.GF4043@hirez.programming.kicks-ass.net> From: Dou Liyang Message-ID: Date: Fri, 6 Apr 2018 16:42:14 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <20180403112311.GF4043@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="gbk"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.106] X-yoursite-MailScanner-ID: 93A394D0EFF5.A9F89 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: douly.fnst@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, Peter, At 04/03/2018 07:23 PM, Peter Zijlstra wrote: > On Tue, Apr 03, 2018 at 12:25:56PM +0200, Thomas Gleixner wrote: >> On Mon, 2 Apr 2018, Li RongQing wrote: >> >>> lots of application will read /proc/stat, like ps and vmstat, but we >>> find the reading time are spreading on Purley platform which has lots >>> of possible CPUs and interrupt. >>> >>> To reduce the reading time, only scan the present CPUs, not all possible >>> CPUs, which speeds the reading of /proc/stat 20 times on Purley platform >>> which has 56 present CPUs, and 224 possible CPUs >> >> Why is BIOS/ACPI telling the kernel that there are 224 possible CPUs unless >> it supports physical CPU hotplug. > > BIOS is crap, news at 11. I've got boxes like that too. Use > possible_cpu=$nr if you're bothered by it -- it's what I do. > Yes, I think so. it is a manual way to reset the number. For this situation, I am investigating to restrict the number of possible CPUs automatically, But, due to the limitation of ACPI subsystem, I can do it _before_ setup_percpu_area where the number will be used. But, I can provider an indicator to tell the system that whether the physical CPU hotplug is support or not later. Can we use this indicator like that in this situation: if ture Using for_each_possible_cpu(cpu) else Using for_each_present_cpu(cpu) Thanks, dou > >