From owner-freebsd-hackers@freebsd.org Thu Aug 23 08:39:56 2018 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 42F38108601C for ; Thu, 23 Aug 2018 08:39:56 +0000 (UTC) (envelope-from sebastian.huber@embedded-brains.de) Received: from dedi548.your-server.de (dedi548.your-server.de [85.10.215.148]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CEDF487651 for ; Thu, 23 Aug 2018 08:39:55 +0000 (UTC) (envelope-from sebastian.huber@embedded-brains.de) Received: from [78.46.172.3] (helo=sslproxy06.your-server.de) by dedi548.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.85_2) (envelope-from ) id 1fsl9f-0003A4-DB for freebsd-hackers@freebsd.org; Thu, 23 Aug 2018 10:39:47 +0200 Received: from [82.135.62.35] (helo=mail.embedded-brains.de) by sslproxy06.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1fsl9f-000KsL-6X for freebsd-hackers@freebsd.org; Thu, 23 Aug 2018 10:39:47 +0200 Received: from localhost (localhost.localhost [127.0.0.1]) by mail.embedded-brains.de (Postfix) with ESMTP id 0F8DC2A165C for ; Thu, 23 Aug 2018 10:39:50 +0200 (CEST) Received: from mail.embedded-brains.de ([127.0.0.1]) by localhost (zimbra.eb.localhost [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id invQAVaKo4Md for ; Thu, 23 Aug 2018 10:39:49 +0200 (CEST) Received: from localhost (localhost.localhost [127.0.0.1]) by mail.embedded-brains.de (Postfix) with ESMTP id AC8952A167F for ; Thu, 23 Aug 2018 10:39:49 +0200 (CEST) X-Virus-Scanned: amavisd-new at zimbra.eb.localhost Received: from mail.embedded-brains.de ([127.0.0.1]) by localhost (zimbra.eb.localhost [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id V96JebRsKgIB for ; Thu, 23 Aug 2018 10:39:49 +0200 (CEST) Received: from [192.168.96.149] (unknown [192.168.96.149]) by mail.embedded-brains.de (Postfix) with ESMTPSA id 87D342A165C for ; Thu, 23 Aug 2018 10:39:49 +0200 (CEST) Subject: Re: epoch(9) background information? From: Sebastian Huber To: FreeBSD References: Message-ID: <3bfedcc3-0dae-7979-2bd4-da83f2c67e87@embedded-brains.de> Date: Thu, 23 Aug 2018 10:39:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: quoted-printable X-Authenticated-Sender: smtp-embedded@poldinet.de X-Virus-Scanned: Clear (ClamAV 0.100.1/24865/Thu Aug 23 07:52:53 2018) X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.27 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Aug 2018 08:39:56 -0000 On 21/08/18 14:33, Sebastian Huber wrote: > Hello, > > I update currently a port of the FreeBSD network stack, etc. to the=20 > real-time operating system RTEMS from the head version at 2017-04-04=20 > to the head version of today. I noticed that some read-write locks are=20 > replaced by a relatively new stuff called EPOCH(9). Is there some=20 > background information available for this? The man page is a bit vague=20 > and searching for something named epoch on the internet is not really=20 > great. For example, what is the motivation for this change? How is=20 > this related to read-copy-update (RCU)? > We used the FreeBSD network stack also on low-end targets=20 (uni-processor) such as MCF548x ColdFire, Atmel SAM V71, SPARC LEON,=20 etc. in current production environments (not legacy systems). The=20 introduction of lock-free data structures (Concurrency Kit) and this=20 epoch memory reclamation makes little sense on these targets (at least=20 from my point of view). However, FreeBSD has still the SMP configuration=20 option (sys/conf/options) which suggests that SMP is optional. Is a=20 uni-processor system something which is considered by the FreeBSD=20 community as a thing worth supporting or can I expect that this is an=20 exotic environment which will get less and less well supported in the=20 future? I just need some guidance so that I can better plan for future=20 FreeBSD baseline updates. --=20 Sebastian Huber, embedded brains GmbH Address : Dornierstr. 4, D-82178 Puchheim, Germany Phone : +49 89 189 47 41-16 Fax : +49 89 189 47 41-09 E-Mail : sebastian.huber@embedded-brains.de PGP : Public key available on request. Diese Nachricht ist keine gesch=C3=A4ftliche Mitteilung im Sinne des EHUG= .