From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id /jxeCdjTzGBxUAAAWB0awg (envelope-from ) for ; Fri, 18 Jun 2021 13:11:52 -0400 Received: by simark.ca (Postfix, from userid 112) id 029321F163; Fri, 18 Jun 2021 13:11:52 -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 74BF41E939 for ; Fri, 18 Jun 2021 13:11:50 -0400 (EDT) Received: from lists-lttng01.efficios.com (localhost [IPv6:::1]) by lists.lttng.org (Postfix) with ESMTP id 4G657S64qKzJSx; Fri, 18 Jun 2021 13:11:48 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1624036309; bh=CKmAK0AdUFBmKGPuIs2EZE+RE6hPLkMtKS+A2dSBmP0=; h=Date:To:In-Reply-To:References:Subject:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=1BTbvro/XAzBt55750xqvCKANZrCtlVcpeFDqfnEruFSVa0zS6YMdqIBilxSCPQna rXim0WycLXufrwvS5lCdUyU8Tc4FPHrVhciCkTcKpp9DflWwJYrTIbQ6shWJSazzax 4SFiy4JhsCoHjPtmzu+S0rNAm9t+16brW4GlzrtuXKO4jlENBCvyf8nzakAKUXHXUy 2Tex2GaRYXM+jwWjP+HH7648Cs9CVDSeiqIGtmrfNrCtnfjVahRZmg9zfpIo1Z+YNz ZksH/0Nom1gxw6esGybLwrX7d1ve6sulgd+zNuG9PL3Sr2rPlWsgeBo8idnydqGmeB nYI8Gb1tnHmDQ== Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by lists.lttng.org (Postfix) with ESMTPS id 4G657R5LNgzJSw for ; Fri, 18 Jun 2021 13:11:47 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 73649345F05; Fri, 18 Jun 2021 13:11:41 -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 Y8lnZ78Fy1sc; Fri, 18 Jun 2021 13:11:37 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 0B9D2345F04; Fri, 18 Jun 2021 13:11:37 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 0B9D2345F04 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 haVpbEZVXE3U; Fri, 18 Jun 2021 13:11:37 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id F143B345D37; Fri, 18 Jun 2021 13:11:36 -0400 (EDT) Date: Fri, 18 Jun 2021 13:11:36 -0400 (EDT) To: Norbert Lange Message-ID: <424774796.12773.1624036296954.JavaMail.zimbra@efficios.com> In-Reply-To: References: MIME-Version: 1.0 X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4018 (ZimbraWebClient - FF89 (Linux)/8.8.15_GA_4026) Thread-Topic: Disabling sys_membarrier in lttng urcu Thread-Index: fTkCbu8ZNTvPu1TjWhQtg44hRtSm7w== Subject: Re: [lttng-dev] Disabling sys_membarrier in lttng urcu 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 Cc: lttng-dev Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" ----- On Jun 17, 2021, at 6:13 PM, lttng-dev lttng-dev@lists.lttng.org wrote: > Hello, > > Some old topic, see > https://lists.lttng.org/pipermail/lttng-dev/2019-November/029411.html. > (I actually thought this was solved meanwhile). > > With lttng 2.13 liburcu is replicated in lttng-ust so my old custom > hack aint helping. > > Aside from another crude hack, I thought about doing this: > > extern int lttng_ust_urcu_has_sys_membarrier; > int setup() { > lttng_ust_urcu_has_sys_membarrier = 0; > } > > this is obvious possible in my own program, but I don't know if some > lttng daemon would need to update RCU structures in shared memory that > should sync to other processes (and wont do that with sys_membarrier > in case of Xenomai threads)? > > Seems safer to me to hack it out once more... We currently don't have any RCU synchronization across shared memory, and the implementation we have in lttng-ust only tracks threads within the same process, so it would be safe to tweak the lttng-ust-urcu behavior to use membarrier or not based on an environment variable. So I think we could expose a new "--disable-sys-membarrier" configure option to lttng-ust, and maybe add a LTTNG_UST_MEMBARRIER environment variable. This would likely be 2.14 material though. I also notice that lttng-ust 2.13's implementation of RCU still refers to CONFIG_RCU_FORCE_SYS_MEMBARRIER which belongs to liburcu. This is probably something we'll want to fix right away before we release 2.13 final. 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