From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3D7FC3279B for ; Fri, 6 Jul 2018 06:10:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A2E82404E for ; Fri, 6 Jul 2018 06:10:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3A2E82404E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=c-sky.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753625AbeGFGJz (ORCPT ); Fri, 6 Jul 2018 02:09:55 -0400 Received: from smtp2200-217.mail.aliyun.com ([121.197.200.217]:45030 "EHLO smtp2200-217.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753457AbeGFGHv (ORCPT ); Fri, 6 Jul 2018 02:07:51 -0400 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.0750676|-1;CH=green;FP=0|0|0|0|0|-1|-1|-1;HT=e02c03308;MF=ren_guo@c-sky.com;NM=1;PH=DS;RN=12;RT=12;SR=0;TI=SMTPD_---.CMxpOBn_1530857260; Received: from localhost(mailfrom:ren_guo@c-sky.com fp:SMTPD_---.CMxpOBn_1530857260) by smtp.aliyun-inc.com(10.147.44.118); Fri, 06 Jul 2018 14:07:40 +0800 Date: Fri, 6 Jul 2018 14:07:40 +0800 From: Guo Ren To: Peter Zijlstra Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, daniel.lezcano@linaro.org, jason@lakedaemon.net, arnd@arndb.de, c-sky_gcc_upstream@c-sky.com, gnu-csky@mentor.com, thomas.petazzoni@bootlin.com, wbx@uclibc-ng.org, green.hu@gmail.com Subject: Re: [PATCH V2 16/19] csky: SMP support Message-ID: <20180706060740.GB8707@guoren> References: <21d859826fe19aecaa2aefe3103d6d33e6f1b925.1530465326.git.ren_guo@c-sky.com> <20180705180503.GH2530@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180705180503.GH2530@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 05, 2018 at 08:05:03PM +0200, Peter Zijlstra wrote: > On Mon, Jul 02, 2018 at 01:30:19AM +0800, Guo Ren wrote: > > +static irqreturn_t handle_ipi(int irq, void *dev) > > +{ > > + unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits; > > + > > + while (true) { > > + unsigned long ops; > > + > > + /* Order bit clearing and data access. */ > > + mb(); > > + > > + ops = xchg(pending_ipis, 0); > > + if (ops == 0) > > + return IRQ_HANDLED; > > + > > + if (ops & (1 << IPI_RESCHEDULE)) > > + scheduler_ipi(); > > + > > + if (ops & (1 << IPI_CALL_FUNC)) > > + generic_smp_call_function_interrupt(); > > + > > + BUG_ON((ops >> IPI_MAX) != 0); > > + > > + /* Order data access and bit testing. */ > > + mb(); > > + } > > + > > + return IRQ_HANDLED; > > +} > > + > > +static void (*send_arch_ipi)(const unsigned long *mask, unsigned long irq) = NULL; > > + > > +void __init set_send_ipi(void (*func)(const unsigned long *, unsigned long)) > > +{ > > + if (send_arch_ipi) > > + return; > > + > > + send_arch_ipi = func; > > +} > > + > > +static void > > +send_ipi_message(const struct cpumask *to_whom, enum ipi_message_type operation) > > +{ > > + int i; > > + > > + mb(); > > + for_each_cpu(i, to_whom) > > + set_bit(operation, &ipi_data[i].bits); > > + > > + mb(); > > + send_arch_ipi(cpumask_bits(to_whom), IPI_IRQ); > > +} > > > Please explain those mb()'s... I'm thinking you meant to use smp_mb(). Yes, smp_mb(). Current smp_mb()&mb() is the same: sync.is. In next version patch, I'll seperate smp_mb() and mb() and use ld/st.barrier instead of sync.is. Sync.is is expensive that it flush cpu's pipeline. > But then for handle_ipi(), the xchg() should already imply all those. Yes, approve. > And the send_ipi_message() only needs the second. Yes, approve. Guo Ren