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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E669C433EF for ; Wed, 29 Sep 2021 03:11:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F291E613CF for ; Wed, 29 Sep 2021 03:11:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243769AbhI2DMR (ORCPT ); Tue, 28 Sep 2021 23:12:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:59260 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230022AbhI2DMG (ORCPT ); Tue, 28 Sep 2021 23:12:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632885025; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ZXdkycR73/zNfkluTLeMsLWh81UPqs6kxv2+DoxeOwQ=; b=Ra8F7Zcqpni7COrDfAAdB68lQY7JBrknQ95cfxR5Pmct5p2aB91VyHIae4n/l1GPQUypvh ZqPMl2HERFjMRAswoHoXGlegfGRUX3tDf8VOqz31wGCNyuYJqPcowBaQD5Quh8KEzMyJbq AX7s0cnfafC+QYNYL9OfXBHmNNqAKoE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-515-LSPGNI3YNwuJdkZ2_Hnndg-1; Tue, 28 Sep 2021 23:10:23 -0400 X-MC-Unique: LSPGNI3YNwuJdkZ2_Hnndg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7B8D6824FA9; Wed, 29 Sep 2021 03:10:21 +0000 (UTC) Received: from piliu.users.ipa.redhat.com (ovpn-8-24.pek2.redhat.com [10.72.8.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7A0AF19C79; Wed, 29 Sep 2021 03:10:16 +0000 (UTC) Date: Wed, 29 Sep 2021 11:10:11 +0800 From: Pingfan Liu To: Mark Rutland Cc: Pingfan Liu , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Marc Zyngier , Joey Gouly , Sami Tolvanen , Julien Thierry , Thomas Gleixner , Yuichi Ito , linux-kernel@vger.kernel.org Subject: Re: [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64 Message-ID: References: <20210924132837.45994-1-kernelfans@gmail.com> <20210924132837.45994-5-kernelfans@gmail.com> <20210928091053.GD1924@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210928091053.GD1924@C02TD0UTHF1T.local> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 28, 2021 at 10:10:53AM +0100, Mark Rutland wrote: > On Fri, Sep 24, 2021 at 09:28:36PM +0800, Pingfan Liu wrote: > > The call to rcu_irq_enter() originated from gic_handle_irq() is > > redundant now, since arm64 has enter_from_kernel_mode() akin to > > irqenter_entry(), which has already called rcu_irq_enter(). > > Here I think you're referring to the call in handle_domain_irq(), but > that isn't clear from the commit message. > Yes, and I will make it clear in V2. > > Based on code analysis, the redundant can raise some mistake, e.g. > > rcu_data->dynticks_nmi_nesting inc 2, which causes > > rcu_is_cpu_rrupt_from_idle() unexpected. > > > > So eliminate the call to irq_enter() in handle_domain_irq(). And > > accordingly supplementing irq_enter_rcu(). > > We support many more irqchips on arm64, and GICv3 can be used on regular > 32-bit arm, so this isn't right. Moving the irq_enter_rcu() call > into the GICv3 driver specifically breaks other drivers on arm64 by > removing the call, and breaks the GICv3 driver on arm by adding a > duplicate call. > Oops. I forgot to protect the code in GICv3 with CONFIG_HAVE_ARCH_IRQENTRY > It looks like this should live in do_interrupt_handler() in > arch/arm64/kernel/entry-common.c, e.g. > > | static void do_interrupt_handler(struct pt_regs *regs, > | void (*handler)(struct pt_regs *)) > | { > | irq_enter_rcu(); > | if (on_thread_stack()) > | call_on_irq_stack(regs, handler); > | else > | handler(regs); > | irq_exit_rcu(); > | } > > ... unless there's some problem with that? > Yeah, do_interrupt_handler() is a more suitable place. But to resolve the performance regression of rescheduling IPI [1], it is badly demanded to distinguish irqnr before calling irq_enter_rcu() (please see 5/5 and [2] for the context). So it is a compromise to host the code in GICv3. Any good idea? [1]: https://lore.kernel.org/linux-arm-kernel/20201101131430.257038-1-maz@kernel.org/ [2]: https://lore.kernel.org/linux-arm-kernel/87lfewnmdz.fsf@nanos.tec.linutronix.de/ Thanks, Pingfan