From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751400AbcEIQ4H (ORCPT ); Mon, 9 May 2016 12:56:07 -0400 Received: from www.linutronix.de ([62.245.132.108]:39322 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751040AbcEIQ4G (ORCPT ); Mon, 9 May 2016 12:56:06 -0400 Date: Mon, 9 May 2016 18:54:14 +0200 (CEST) From: Thomas Gleixner To: Tetsuo Handa cc: peterz@infradead.org, mingo@kernel.org, akpm@linux-foundation.org, mgorman@techsingularity.net, mhocko@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: x86_64 Question: Are concurrent IPI requests safe? In-Reply-To: <201605092354.AHF82313.FtQFOMVOFJLOSH@I-love.SAKURA.ne.jp> Message-ID: References: <201605061958.HHG48967.JVFtSLFQOFOOMH@I-love.SAKURA.ne.jp> <201605092354.AHF82313.FtQFOMVOFJLOSH@I-love.SAKURA.ne.jp> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 9 May 2016, Tetsuo Handa wrote: > > It seems to me that APIC_BASE APIC_ICR APIC_ICR_BUSY are all constant > regardless of calling cpu. Thus, native_apic_mem_read() and > native_apic_mem_write() are using globally shared constant memory > address and __xapic_wait_icr_idle() is making decision based on > globally shared constant memory address. Am I right? No. The APIC address space is per cpu. It's the same address but it's always accessing the local APIC of the cpu on which it is called. Thanks, tglx