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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1DB3AC77B75 for ; Tue, 9 May 2023 11:37:01 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.532124.828160 (Exim 4.92) (envelope-from ) id 1pwLe0-00082g-Ba; Tue, 09 May 2023 11:36:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 532124.828160; Tue, 09 May 2023 11:36:36 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1pwLe0-00082Z-8t; Tue, 09 May 2023 11:36:36 +0000 Received: by outflank-mailman (input) for mailman id 532124; Tue, 09 May 2023 11:36:34 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1pwLdy-00082T-ON for xen-devel@lists.xenproject.org; Tue, 09 May 2023 11:36:34 +0000 Received: from desiato.infradead.org (desiato.infradead.org [2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id bfebc1a3-ee5d-11ed-b227-6b7b168915f2; Tue, 09 May 2023 13:36:34 +0200 (CEST) Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pwLdH-00678Y-0c; Tue, 09 May 2023 11:35:52 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8F613302F3D; Tue, 9 May 2023 13:35:48 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6D04F20C342B1; Tue, 9 May 2023 13:35:48 +0200 (CEST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: bfebc1a3-ee5d-11ed-b227-6b7b168915f2 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=9uy06VylNOBEAiDOc+c/ggtZsNSxY44p/M1PWpIHlTo=; b=AdPs8XtYEpkR3G25UQ9/ynnaJQ yoQ7TJHtTer78qTxQSruGfUSIJdNhTXt+0UcvF9ygN5qgsE6skCGKlKdAU+XGBlszdQLENogWL1pZ XLDEoXkr1kINeJ7StBwuvXlWsxIhr3i/RPNAsp79LBG8KMNp3MRdGeYKSudMDFtBS86uE8nzWEe5v a8CfaEawnbrmqXklNcksitW8TUN0x1wEip6a7zDZlkdKaRBllociBadnbaExT9c9ou3QCvpRH4AgG bSH5gSP2c1D5dxXxDWXZkTYGeRAN4a/hJ1z/YW9bJKB/4Im2NbAtVPF75WnxH6OHWaCKH0GsK31IY N6mfY+UQ==; Date: Tue, 9 May 2023 13:35:48 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: LKML , x86@kernel.org, David Woodhouse , Andrew Cooper , Brian Gerst , Arjan van de Veen , Paolo Bonzini , Paul McKenney , Tom Lendacky , Sean Christopherson , Oleksandr Natalenko , Paul Menzel , "Guilherme G. Piccoli" , Piotr Gorski , Usama Arif , Juergen Gross , Boris Ostrovsky , xen-devel@lists.xenproject.org, Russell King , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Guo Ren , linux-csky@vger.kernel.org, Thomas Bogendoerfer , linux-mips@vger.kernel.org, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Paul Walmsley , Palmer Dabbelt , linux-riscv@lists.infradead.org, Mark Rutland , Sabin Rapan , "Michael Kelley (LINUX)" Subject: Re: [patch v3 18/36] [patch V2 18/38] cpu/hotplug: Add CPU state tracking and synchronization Message-ID: <20230509113548.GD38236@hirez.programming.kicks-ass.net> References: <20230508181633.089804905@linutronix.de> <20230508185218.240871842@linutronix.de> <20230509110722.GZ83892@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230509110722.GZ83892@hirez.programming.kicks-ass.net> On Tue, May 09, 2023 at 01:07:23PM +0200, Peter Zijlstra wrote: > On Mon, May 08, 2023 at 09:43:55PM +0200, Thomas Gleixner wrote: > > > +static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state) > > +{ > > + atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state); > > + int sync = atomic_read(st); > > + > > + while (!atomic_try_cmpxchg(st, &sync, state)); > > +} > > Why isn't: > > atomic_set(st, state); > > any good? Hmm, should at the very least be atomic_set_release(), but if you want the full barrier then: (void)atomic_xchg(st, state); is the much saner way to write the above.