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.lttng.org (lists.lttng.org [167.114.26.123]) (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 44593EB64DA for ; Thu, 22 Jun 2023 20:11:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1687464660; bh=mtX84/pgKFtIE/28HQ8DGYwKdkuSRFh9KOSrqfnrVL8=; h=To:Cc:In-Reply-To:References:Date:Subject:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From:Reply-To:From; b=J2sx/NIxVpga2+eNYLUCBKHyibOO1Jds3cEuRgZ2BuhtUuMn0tTO3gtURr7igzjGg RA5KHfrjWwNNKdvUR9SqOqqghnZt/36tFhSQ+nAdrD5PSAFMx+6llZji2/6NhjVJr4 Vm6flHW6OFIh3nVX1HcvrG6PcDnQdfI0+IqiIiwXzyC6osmT89yIuUHF0L+MH90rTN CNBnEVx62dAkL0zI1Cyfg4hL0dKwme+gl0cHeaRtvmC66bNMmHErEbMrL4jywDmMzj e1G4gBeWfZ7QjzPseNkxhWFa4plhDSIdaGnZOn58IjLbggTtNHQFrlNPEnFMQyhOfr 44EUh9jiicmGw== Received: from lists-lttng01.efficios.com (localhost [IPv6:::1]) by lists.lttng.org (Postfix) with ESMTP id 4QnBMR6KS5z20Qc; Thu, 22 Jun 2023 16:10:59 -0400 (EDT) Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by lists.lttng.org (Postfix) with ESMTPS id 4QnBMR15qHz20QZ for ; Thu, 22 Jun 2023 16:10:59 -0400 (EDT) Received: from localhost (modemcable094.169-200-24.mc.videotron.ca [24.200.169.94]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4QnBMP2nXjz191Z; Thu, 22 Jun 2023 16:10:57 -0400 (EDT) To: Mathieu Desnoyers , paulmck@kernel.org Cc: lttng-dev@lists.lttng.org In-Reply-To: <9e5fbcf0-bf3d-c0b3-c45b-2e440e8276e1@efficios.com> Organization: EfficiOS References: <20230515201718.9809-1-odion@efficios.com> <20230515201718.9809-3-odion@efficios.com> <105bad2a-9fed-4353-a434-a571ce9da7ac@paulmck-laptop> <87zg4rl1du.fsf@laura> <9e5fbcf0-bf3d-c0b3-c45b-2e440e8276e1@efficios.com> Date: Thu, 22 Jun 2023 16:10:57 -0400 Message-ID: <87v8ffl0ku.fsf@laura> MIME-Version: 1.0 Subject: Re: [lttng-dev] [PATCH 02/11] urcu/uatomic: Use atomic builtins if configured X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.39 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Olivier Dion via lttng-dev Reply-To: Olivier Dion Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" On Thu, 22 Jun 2023, Mathieu Desnoyers wrote: > On 6/22/23 15:53, Olivier Dion wrote: >> On Thu, 22 Jun 2023, "Paul E. McKenney" wrote: >> >>> I suggest C11 volatile atomic load/store. Load/store fusing is permitted >>> for non-volatile atomic loads and stores, and such fusing can ruin your >>> code's entire day. ;-) >> >> Good catch. Seems like not a problem on GCC (yet), but Clang is extremely >> aggressive and seems to do store fusing on some corner cases [0]. > > I don't think this is an example of store fusing, but rather just that > the compiler can eliminate stores to static variables which are > otherwise unused, making the entire variable useless. Indeed, that is not store fusing. It is however interesting to see that the dead store elimination is avoid when casting one of the &x with a volatile qualifier. TIL dead store can apply to atomics. -- Olivier Dion EfficiOS Inc. https://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev