From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 6FD2D7D8A4 for ; Sun, 12 May 2019 01:09:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726338AbfELBJw (ORCPT ); Sat, 11 May 2019 21:09:52 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:34423 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726393AbfELBJw (ORCPT ); Sat, 11 May 2019 21:09:52 -0400 Received: by mail-wr1-f68.google.com with SMTP id f8so1817499wrt.1 for ; Sat, 11 May 2019 18:09:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=b8AW4BGaZt47ssLrB6qXfhhNxNJaIAABugP8Bf2LUJc=; b=JtUgc6MIGk7Y5MmFv4m3d4ISHMCOvUp6g70RA6sbJklbPEVGXVcftsBCT7hb5H1h0k /tp84iZt9wpGTu4789QOwr/LuvvL5efzMDvkcNfztOA+KYtq22DXr4TJOuCD71vDgcfy PAmm6OmFKtJSdn20Sq0KP1N7R6yfVj4Vk6Oss= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=b8AW4BGaZt47ssLrB6qXfhhNxNJaIAABugP8Bf2LUJc=; b=romgGiy/mCuJI6tF23zBYCYZiexyaxLdZFIcclw6leLBXP/Ikmcdk0iYbpZEbozkv2 Uld6LNPBPxlgzA55n88ABGw/Df58bzlzUBipZd4km2VOOZ6e//EYXlklNsEdR27Cor20 PIRXCe4xHzjOxOvLkJKJID0ntylyHB9/fMPMJoXeBTKbzZhwqakbNz9vNbuEPHDKfKrF snOu4vN3G3apiBwFXpkzqzQuNs7qIdupWhwElyrZNPbcoUGa6fNpz1WFg0BWvUouEmlV SWpvRL6pNdJ0Pi1mU0oFEbbYgtdstGJvEVhaewKAF9Jd422s+LOLPL2nwByfBV+wClcS c/lw== X-Gm-Message-State: APjAAAUeB79tEuQPDldaovHvK1HWCKsHDNbU+qq3q73nTNoBsTpc8Wdy hlTW+T91ZWiraPFnirhdX4k58A== X-Google-Smtp-Source: APXvYqyhFbsf1FNgNI+/rAhBZzMgj02SE5lckYXHhdIt2dVUQv5+Ig7Tv7vgFOweYh2jEJHIGNHKzg== X-Received: by 2002:a5d:4647:: with SMTP id j7mr7970362wrs.280.1557623389777; Sat, 11 May 2019 18:09:49 -0700 (PDT) Received: from andrea ([89.22.71.151]) by smtp.gmail.com with ESMTPSA id t18sm19424094wrg.19.2019.05.11.18.09.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 11 May 2019 18:09:49 -0700 (PDT) Date: Sun, 12 May 2019 03:09:41 +0200 From: Andrea Parri To: "Paul E. McKenney" Cc: Joel Fernandes , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Jonathan Corbet , linux-doc@vger.kernel.org Subject: Re: [PATCH] doc/rcu: Correct field_count field naming in examples Message-ID: <20190512010941.GA8611@andrea> References: <20190505020328.165839-1-joel@joelfernandes.org> <20190507000453.GB3923@linux.ibm.com> <20190508162635.GD187505@google.com> <20190508181638.GY3923@linux.ibm.com> <20190511221126.GA3984@andrea> <20190512004131.GE3923@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190512004131.GE3923@linux.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Sat, May 11, 2019 at 05:41:31PM -0700, Paul E. McKenney wrote: > On Sun, May 12, 2019 at 12:11:26AM +0200, Andrea Parri wrote: > > Hi Paul, Joel, > > > > > > > On the other hand, would you have ideas for more modern replacement > > > > > examples? > > > > > > > > There are 3 cases I can see in listRCU.txt: > > > > (1) action taken outside of read_lock (can tolerate stale data), no in-place update. > > > > this is the best possible usage of RCU. > > > > (2) action taken outside of read_lock, in-place updates > > > > this is good as long as not too many in-place updates. > > > > involves copying creating new list node and replacing the > > > > node being updated with it. > > > > (3) cannot tolerate stale data: here a deleted or obsolete flag can be used > > > > protected by a per-entry lock. reader > > > > aborts if object is stale. > > > > > > > > Any replacement example must make satisfy (3) too? > > > > > > It would be OK to have a separate example for (3). It would of course > > > be nicer to have one example for all three, but not all -that- important. > > > > > > > The only example for (3) that I know of is sysvipc sempahores which you also > > > > mentioned in the paper. Looking through this code, it hasn't changed > > > > conceptually and it could be a fit for an example (ipc_valid_object() checks > > > > for whether the object is stale). > > > > > > That is indeed the classic canonical example. ;-) > > > > > > > The other example could be dentry look up which uses seqlocks for the > > > > RCU-walk case? But that could be too complex. This is also something I first > > > > learnt from the paper and then the excellent path-lookup.rst document in > > > > kernel sources. > > > > > > This is a great example, but it would need serious simplification for > > > use in the Documentation/RCU directory. Note that dcache uses it to > > > gain very limited and targeted consistency -- only a few types of updates > > > acquire the write-side of that seqlock. > > > > > > Might be quite worthwhile to have a simplified example, though! > > > Perhaps a trivial hash table where write-side sequence lock is acquired > > > only when moving an element from one chain to another? > > > > Sorry to take you down here..., but what do you mean by "the paper"? ;-/ > > One or both of these two: > > http://www2.rdrop.com/~paulmck/techreports/survey.2012.09.17a.pdf > http://www2.rdrop.com/~paulmck/techreports/RCUUsage.2013.02.24a.pdf Oh, these are familiar. ;-) Thank you! Andrea