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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 59417C43331 for ; Wed, 13 Nov 2019 00:22:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 278DC21872 for ; Wed, 13 Nov 2019 00:22:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573604561; bh=KYsxxVfb9c/zNMVXXf6w4bZXIsHRXJu0HaUT9jvjS00=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=RZX9qIz5EbD5lyDwc3A9BzWOw2eZksQn1gBlCmbctIDVUUKvTjHqJ9AVvK9v1W9LE msOfPnP+Sw1oloJysQ1oZDlhaJEl818FMM2ONbhxEtCfdsHqcac8cfhc2zA1yNL2X0 C6EyOnRlx2g0qg9q4QI8dgvMAuIN5P6LJ7XaDxyA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726969AbfKMAWk (ORCPT ); Tue, 12 Nov 2019 19:22:40 -0500 Received: from mail.kernel.org ([198.145.29.99]:58420 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726910AbfKMAWk (ORCPT ); Tue, 12 Nov 2019 19:22:40 -0500 Received: from localhost (lfbn-ncy-1-150-155.w83-194.abo.wanadoo.fr [83.194.232.155]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AD8CA206BB; Wed, 13 Nov 2019 00:22:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573604559; bh=KYsxxVfb9c/zNMVXXf6w4bZXIsHRXJu0HaUT9jvjS00=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X60QwV+TY1luo9vcFS/kOlrxatdJKJF4PDOBVlOrneBwPxse7QBb6ZbrqZqNYAaSJ klLbWbH9v36NACYd+CGLcLlxIw6gkJkEH9QIEMNLiOvNfezKtJ05omywy2QM0i/iWa GFkKAX5BjMUUmQVcipBXgLeYBT2pI3FAfhPUPSXs= Date: Wed, 13 Nov 2019 01:22:36 +0100 From: Frederic Weisbecker To: Leonard Crestez Cc: Peter Zijlstra , Ingo Molnar , LKML , "Paul E . McKenney" , Thomas Gleixner , Viresh Kumar , "linux-pm@vger.kernel.org" , Stephen Rothwell Subject: Re: [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing Message-ID: <20191113002235.GA5746@lenoir> References: <20191108160858.31665-1-frederic@kernel.org> <20191108160858.31665-4-frederic@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Tue, Nov 12, 2019 at 08:27:05PM +0000, Leonard Crestez wrote: > On 08.11.2019 18:09, Frederic Weisbecker wrote: > > Instead of fetching the value of flags and perform an xchg() to clear > > a bit, just use atomic_fetch_andnot() that is more suitable to do that > > job in one operation while keeping the full ordering. > > > > Signed-off-by: Frederic Weisbecker > > Cc: Paul E. McKenney > > Cc: Thomas Gleixner > > Cc: Peter Zijlstra > > Cc: Ingo Molnar > > --- > > kernel/irq_work.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/irq_work.c b/kernel/irq_work.c > > index 255454a48346..49c53f80a13a 100644 > > --- a/kernel/irq_work.c > > +++ b/kernel/irq_work.c > > @@ -34,7 +34,7 @@ static bool irq_work_claim(struct irq_work *work) > > oflags = atomic_fetch_or(IRQ_WORK_CLAIMED, &work->flags); > > /* > > * If the work is already pending, no need to raise the IPI. > > - * The pairing atomic_xchg() in irq_work_run() makes sure > > + * The pairing atomic_fetch_andnot() in irq_work_run() makes sure > > * everything we did before is visible. > > */ > > if (oflags & IRQ_WORK_PENDING) > > @@ -135,7 +135,6 @@ static void irq_work_run_list(struct llist_head *list) > > { > > struct irq_work *work, *tmp; > > struct llist_node *llnode; > > - int flags; > > > > BUG_ON(!irqs_disabled()); > > > > @@ -144,6 +143,7 @@ static void irq_work_run_list(struct llist_head *list) > > > > llnode = llist_del_all(list); > > llist_for_each_entry_safe(work, tmp, llnode, llnode) { > > + int flags; > > /* > > * Clear the PENDING bit, after this point the @work > > * can be re-used. > > @@ -151,8 +151,7 @@ static void irq_work_run_list(struct llist_head *list) > > * to claim that work don't rely on us to handle their data > > * while we are in the middle of the func. > > */ > > - flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING; > > - atomic_xchg(&work->flags, flags); > > + flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags); > > > > work->func(work); > > /* > > This breaks switching between cpufreq governors in linux-next on arm64 > and various other stuff. The fix in this email doesn't compile: > > https://lkml.org/lkml/2019/11/12/622 > > I assume you meant "&= ~" instead of "~=", this seems to work: Indeed, duh again! I still think that ~= would be nice to have though... Thanks! > > diff --git a/kernel/irq_work.c b/kernel/irq_work.c > index 49c53f80a13a..828cc30774bc 100644 > --- a/kernel/irq_work.c > +++ b/kernel/irq_work.c > @@ -156,10 +156,11 @@ static void irq_work_run_list(struct llist_head *list) > work->func(work); > /* > * Clear the BUSY bit and return to the free state if > * no-one else claimed it meanwhile. > */ > + flags &= ~IRQ_WORK_PENDING; > (void)atomic_cmpxchg(&work->flags, flags, flags & > ~IRQ_WORK_BUSY); > } > }