From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id Zz2dDvbleWCUHQAAWB0awg (envelope-from ) for ; Fri, 16 Apr 2021 15:31:02 -0400 Received: by simark.ca (Postfix, from userid 112) id 2E9EC1F104; Fri, 16 Apr 2021 15:31:02 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.2 Received: from lists.lttng.org (lists.lttng.org [167.114.26.123]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 953251E01F for ; Fri, 16 Apr 2021 15:31:01 -0400 (EDT) Received: from lists-lttng01.efficios.com (localhost [IPv6:::1]) by lists.lttng.org (Postfix) with ESMTP id 4FMRC86wL3z1Bk7; Fri, 16 Apr 2021 15:31:00 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1618601461; bh=/0QKFijVyQpMJYZaXoEMepa/3gqFV/lkCyBgUcJHa8I=; h=Date:To:Cc:In-Reply-To:References:Subject:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From:Reply-To:From; b=S+ekU51KWqCccLWpEGpo3qFvH3eWx8b4/IV1JIpZxNHGNAIqA2hhkXHrzMoEwC4XE HRw1qwh9O+w6N8Rv2MRkFwTwV4iJkmCGSJ9FNPGhczHezyxKq02QuyBNiwRC52PrwD DMpx+UKqep0GFW1oekhbekvnUTWuCL7vQPziJ001mEu0qQap9D4sc4ATNs9sYUZz/Y kb8YnqH3QLOTGoZh1Xf0CagAqeaSbnDYG2WCgIs1tJlSazsBaJdsoS3aT8d5DD8lT/ H6ViI+PHq7efoQ/rpd9S0QR/nwLzlFubVn8W3rZKW0YkUTdKuzoFAwMORDUJw0x7Of Yby+EW4LzOQeQ== Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by lists.lttng.org (Postfix) with ESMTPS id 4FMRC84PWMz1Bk1 for ; Fri, 16 Apr 2021 15:31:00 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 4CA6C33A763 for ; Fri, 16 Apr 2021 15:30:54 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id gcgjM8I8umO1; Fri, 16 Apr 2021 15:30:53 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id B7B4133A951; Fri, 16 Apr 2021 15:30:53 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com B7B4133A951 X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 79Qiehg1WzRj; Fri, 16 Apr 2021 15:30:53 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id AA81133A761; Fri, 16 Apr 2021 15:30:53 -0400 (EDT) Date: Fri, 16 Apr 2021 15:30:53 -0400 (EDT) To: paulmck Cc: Peter Zijlstra , Will Deacon , linux-kernel , lttng-dev , Carlos O'Donell Message-ID: <2056094038.84390.1618601453585.JavaMail.zimbra@efficios.com> In-Reply-To: <20210416190244.GJ4212@paulmck-ThinkPad-P17-Gen-1> References: <1680415903.81652.1618584736742.JavaMail.zimbra@efficios.com> <20210416160139.GF4212@paulmck-ThinkPad-P17-Gen-1> <2089952450.84139.1618598408015.JavaMail.zimbra@efficios.com> <20210416190244.GJ4212@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3996 (ZimbraWebClient - FF87 (Linux)/8.8.15_GA_4007) Thread-Topic: liburcu: LTO breaking rcu_dereference on arm64 and possibly other architectures ? Thread-Index: U+jByog9nw+xnur8wetlu9vzLfobNQ== Subject: Re: [lttng-dev] liburcu: LTO breaking rcu_dereference on arm64 and possibly other architectures ? X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Mathieu Desnoyers via lttng-dev Reply-To: Mathieu Desnoyers Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" ----- On Apr 16, 2021, at 3:02 PM, paulmck paulmck@kernel.org wrote: [...] > > If it can be done reasonably, I suggest also having some way for the > person building userspace RCU to say "I know what I am doing, so do > it with volatile rather than memory_order_consume." Like so ? #define CMM_ACCESS_ONCE(x) (*(__volatile__ __typeof__(x) *)&(x)) #define CMM_LOAD_SHARED(p) CMM_ACCESS_ONCE(p) /* * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of * volatile access to implement rcu_dereference rather than * memory_order_consume load from the C11/C++11 standards. * * This may improve performance on weakly-ordered architectures where * the compiler implements memory_order_consume as a * memory_order_acquire, which is stricter than required by the * standard. * * Note that using volatile accesses for rcu_dereference may cause * LTO to generate incorrectly ordered code starting from C11/C++11. */ #ifdef URCU_DEREFERENCE_USE_VOLATILE # define rcu_dereference(x) CMM_LOAD_SHARED(x) #else # if defined (__cplusplus) # if __cplusplus >= 201103L # include # define rcu_dereference(x) ((std::atomic<__typeof__(x)>)(x)).load(std::memory_order_consume) # else # define rcu_dereference(x) CMM_LOAD_SHARED(x) # endif # else # if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) # include # define rcu_dereference(x) atomic_load_explicit(&(x), memory_order_consume) # else # define rcu_dereference(x) CMM_LOAD_SHARED(x) # endif # endif #endif Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev