From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.9 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=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 9DB587D57F for ; Fri, 21 Sep 2018 22:32:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725837AbeIVEXC (ORCPT ); Sat, 22 Sep 2018 00:23:02 -0400 Received: from mail-io1-f66.google.com ([209.85.166.66]:36190 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725756AbeIVEXC (ORCPT ); Sat, 22 Sep 2018 00:23:02 -0400 Received: by mail-io1-f66.google.com with SMTP id q5-v6so13616021iop.3 for ; Fri, 21 Sep 2018 15:32:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=W7G1LyBYm4HSC5qCxaG9wMUa09GRXe4Qr33dj1P3c38=; b=bTijR68FboeRTVFAiAOqUUVXOOXvL8atzI170zC394IEbTNbsAMPfkPwXfsSZjeWKs a5ZgPDElseUuWwDKFLiGWnBxhGs8f/P8ex5DamkFzWyhY8r9Gu4O9ZKbr2Y3F87c2Hn7 qgMIu/sIln9Z/vpL7gHx3iWSrcZUsHMpBItXQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=W7G1LyBYm4HSC5qCxaG9wMUa09GRXe4Qr33dj1P3c38=; b=NGDSCxICsFrGJnEiIl0ff5QhZs4j2UoU2BHzHsH1BXAS09du8Dp7qqjSEmVGYIxAdh abIAGqHGb39JJd1aKGz2X9Je1TMpYBZMAd/+knEXSZ5v4EfWxkw4OYCL5klOhNtZ93ZS uHtPxqvMG6rktiaxDcyZDN/fKjXH574aJ8MJ4ISgrRaJTgr1uhWMm2Ng4D8nUCSUUY6x gUiIxoGOHFvHr4ACZAnQ/oKcFmTiq0s720dHppHAR7VN3PDhK/lb9nENTiQU73s4eS5L PYgubxqc+jVmUYzkk3fzxcGFOIcnb/wpGX3S+DNbPXDSLMhIXxSDWeKt0UesBx/8COT3 JRmA== X-Gm-Message-State: ABuFfog7HtXT8Xfn/gge2cKjEitZ3JT+7hufO6sLlkWT/lc9sSvK48oJ chkmeGobVsfiVbN+jHU4INzepQ== X-Google-Smtp-Source: ACcGV6368inhHgu+ap5tfP0L0acEmPvk/pu4xAZEIOq8KsfmsI5d+1C3/Tj42qXUI1h/0MYOx2cAwA== X-Received: by 2002:a6b:d00b:: with SMTP id x11-v6mr4250604ioa.181.1537569126661; Fri, 21 Sep 2018 15:32:06 -0700 (PDT) Received: from joelaf-glaptop0.roam.corp.google.com ([207.164.22.36]) by smtp.gmail.com with ESMTPSA id b195-v6sm2907320itc.42.2018.09.21.15.32.04 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Sep 2018 15:32:05 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Jonathan Corbet , Josh Triplett , Lai Jiangshan , linux-doc@vger.kernel.org, Mathieu Desnoyers , "Paul E. McKenney" , Steven Rostedt Subject: [PATCH RFC] Documentation: RCU: Clarify comment about fanout Date: Fri, 21 Sep 2018 18:31:53 -0400 Message-Id: <20180921223153.114728-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.19.0.444.g18242da7ef-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org RCU Data-Structures document describes a trick to test RCU with small number of CPUs but with a larger tree. It wasn't immediately clear how the document arrived at 16 CPUs which also requires setting the FANOUT_LEAF to 2 instead of the default of 16. Clarify that. Signed-off-by: Joel Fernandes (Google) --- .../RCU/Design/Data-Structures/Data-Structures.html | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html index 1d2051c0c3fc..791348977da7 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html @@ -127,9 +127,9 @@ CPUs, RCU would configure the rcu_node tree as follows:

RCU currently permits up to a four-level tree, which on a 64-bit system accommodates up to 4,194,304 CPUs, though only a mere 524,288 CPUs for 32-bit systems. -On the other hand, you can set CONFIG_RCU_FANOUT to be -as small as 2 if you wish, which would permit only 16 CPUs, which -is useful for testing. +On the other hand, you can set CONFIG_RCU_FANOUT to be as small as 2 +and set CONFIG_RCU_FANOUT_LEAF to 2 if you wish, which would permit +only 16 CPUs in a 4-level tree. This can be useful for testing.

This multi-level combining tree allows us to get most of the performance and scalability -- 2.19.0.444.g18242da7ef-goog