From patchwork Mon Apr 23 16:42:25 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 8055 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id 5BC5F23E22 for ; Mon, 23 Apr 2012 16:43:12 +0000 (UTC) Received: from mail-iy0-f180.google.com (mail-iy0-f180.google.com [209.85.210.180]) by fiordland.canonical.com (Postfix) with ESMTP id 1DA12A181B8 for ; Mon, 23 Apr 2012 16:43:12 +0000 (UTC) Received: by mail-iy0-f180.google.com with SMTP id e36so23096175iag.11 for ; Mon, 23 Apr 2012 09:43:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-forwarded-to:x-forwarded-for:delivered-to:received-spf:from:to:cc :subject:date:message-id:x-mailer:in-reply-to:references :mime-version:content-type:content-transfer-encoding :x-content-scanned:x-cbid:x-gm-message-state; bh=JLcOpVQBoKmSE+mPDNonZD/aXqOa21IBzdfUnVVdIRw=; b=i7bPxnE6rdrdrmGg1+jDEtQsgbP1j2f5HdFfghSV3ayY/rfImwEjAZkajgn45sgjL0 okCFqLLksi8hBSfxPzVGqiX1pyd7NBY6vE9D6IPOQhI2mV2sRDMg7lbS2kdp+9i+HLbI B22/QZoZGCn9PpbU4yxBvat0LrG/LcpBV3Gt/Z4B1lrFRE6FMSqlkHAfWACOhkuvPQx7 Qh6j+YlcAWq/pIGg1qZqzbhtASQc6K5DXIICQmVz0/VJDEc9KLaVpYDTwu1zoPry+Fi7 jlzNKIDAKAnOt0yKXcwQXcPqEZm5rWkhMTUDz37WaR1VukmjD9BUX6ojw4/PTU+JAysA q/nA== Received: by 10.42.80.19 with SMTP id t19mr2703761ick.55.1335199391861; Mon, 23 Apr 2012 09:43:11 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.231.137.198 with SMTP id x6csp125383ibt; Mon, 23 Apr 2012 09:43:11 -0700 (PDT) Received: by 10.60.1.67 with SMTP id 3mr16061632oek.15.1335199391304; Mon, 23 Apr 2012 09:43:11 -0700 (PDT) Received: from e39.co.us.ibm.com (e39.co.us.ibm.com. [32.97.110.160]) by mx.google.com with ESMTPS id oo4si1311731obc.101.2012.04.23.09.43.11 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 23 Apr 2012 09:43:11 -0700 (PDT) Received-SPF: pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.110.160 as permitted sender) client-ip=32.97.110.160; Authentication-Results: mx.google.com; spf=pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.110.160 as permitted sender) smtp.mail=paulmck@linux.vnet.ibm.com Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 23 Apr 2012 10:43:10 -0600 Received: from d03dlp01.boulder.ibm.com (9.17.202.177) by e39.co.us.ibm.com (192.168.1.139) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Mon, 23 Apr 2012 10:42:48 -0600 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id CD8F2C4000E; Mon, 23 Apr 2012 10:42:43 -0600 (MDT) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q3NGgXuh041246; Mon, 23 Apr 2012 10:42:35 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q3NGgUAn018640; Mon, 23 Apr 2012 10:42:31 -0600 Received: from paulmck-ThinkPad-W500 ([9.47.24.152]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q3NGgTlH018618; Mon, 23 Apr 2012 10:42:29 -0600 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 878FFE5278; Mon, 23 Apr 2012 09:42:29 -0700 (PDT) From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, patches@linaro.org, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 4/6] rcu: Clarify help text for RCU_BOOST_PRIO Date: Mon, 23 Apr 2012 09:42:25 -0700 Message-Id: <1335199347-13926-4-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8 In-Reply-To: <1335199347-13926-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20120423164159.GA13819@linux.vnet.ibm.com> <1335199347-13926-1-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12042316-4242-0000-0000-0000016DB454 X-Gm-Message-State: ALoCoQkxvMSKeHVI2gvQa0noIic1jc7+52ocubAKU0zbHIyURSQ7JatY7WYjjsO4Tx2XZsEUz/yH From: "Paul E. McKenney" The old text confused real-time applications with real-time threads, so that you pretty much needed to understand how this kernel configuration parameter worked to understand the help text. This commit therefore attempts to make the help text human-readable. Reported-by: Jörn Engel Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- init/Kconfig | 23 +++++++++++++++++++---- 1 files changed, 19 insertions(+), 4 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 6cfd71d..85c6870 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -515,10 +515,25 @@ config RCU_BOOST_PRIO depends on RCU_BOOST default 1 help - This option specifies the real-time priority to which preempted - RCU readers are to be boosted. If you are working with CPU-bound - real-time applications, you should specify a priority higher then - the highest-priority CPU-bound application. + This option specifies the real-time priority to which long-term + preempted RCU readers are to be boosted. If you are working + with a real-time application that has one or more CPU-bound + threads running at a real-time priority level, you should set + RCU_BOOST_PRIO to a priority higher then the highest-priority + real-time CPU-bound thread. The default RCU_BOOST_PRIO value + of 1 is appropriate in the common case, which is real-time + applications that do not have any CPU-bound threads. + + Some real-time applications might not have a single real-time + thread that saturates a given CPU, but instead might have + multiple real-time threads that, taken together, fully utilize + that CPU. In this case, you should set RCU_BOOST_PRIO to + a priority higher than the lowest-priority thread that is + conspiring to prevent the CPU from running any non-real-time + tasks. For example, if one thread at priority 10 and another + thread at priority 5 are between themselves fully consuming + the CPU time on a given CPU, then RCU_BOOST_PRIO should be + set to priority 6 or higher. Specify the real-time priority, or take the default if unsure.