From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13676C7112A for ; Sun, 14 Oct 2018 21:30:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B18D420652 for ; Sun, 14 Oct 2018 21:30:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="P3Gvaqcg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B18D420652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=joelfernandes.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726397AbeJOFMa (ORCPT ); Mon, 15 Oct 2018 01:12:30 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:45154 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726186AbeJOFM3 (ORCPT ); Mon, 15 Oct 2018 01:12:29 -0400 Received: by mail-pl1-f196.google.com with SMTP id y15-v6so8273015plr.12 for ; Sun, 14 Oct 2018 14:30:10 -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=B1BhcJksYld0iNAKOWfN53vg1bwHsJCccKOsz1OidCM=; b=P3Gvaqcg09jDvQq63vIOoN9M87VDwdMJuajFEwUh7JleqOSXVfbkOI6OukhN5kvUVr R84d9ws+5LO/PQZkNWjhU/ME1zTIaTwEmCC+QvZXNHS3LWOhEdQZZame1NygElGywAwP Q8rd8Rg4tqBrWmFPcdZaGm5qrEDyVdqFCiBdg= 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=B1BhcJksYld0iNAKOWfN53vg1bwHsJCccKOsz1OidCM=; b=Bt4TZuxfVcq/v/jSxEEqGr1Miqpdg/NoL6Lw79fcI7fRByhYiri+frUJXUH1fPb1rf 2974y9Q3QQ968weDf8v9sX7MPIRn5y1KSfgWHe2MlL0s9fQG5WeKgTY+Af+8w3Z9zry2 f4RVZbEyp9x7RaKrvmvySfX+zjofp4yarBuFchTJxq1fvBozZzIUdVPlHrftgihVsEgU uoTz+IguJLVOBztk2IGwjhxZHwTWoS/7RGN+2K9kvaAf/NOBMTAjcwQ52+VRXt6kJ8fp w7rWEVdJ5HI2uUdraXJ5aOQpbkIEfevSdwSbuXRrXtHK9VeWnp+RXRGV7Ov/wNKENJ2G 6HAw== X-Gm-Message-State: ABuFfohljypEr3Cizr9FcSa239vus73JhO+3J75ykV2JAHLT5qf1M7FN KoVvDeq8tLT+9BQHpCDq6/JBPCEBcz4= X-Google-Smtp-Source: ACcGV61CbYi+gflLdz5Nia99KIF5T4g9v62OzVfZnt+cIHe9yN6/HQTIy1ewdl6j83S1K/p9Bt7hrQ== X-Received: by 2002:a17:902:728e:: with SMTP id d14-v6mr14695117pll.51.1539552609764; Sun, 14 Oct 2018 14:30:09 -0700 (PDT) Received: from joelaf.mtv.corp.google.com ([2620:0:1000:1601:3aef:314f:b9ea:889f]) by smtp.gmail.com with ESMTPSA id h6-v6sm10828804pgn.84.2018.10.14.14.30.06 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 14 Oct 2018 14:30:08 -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] doc: rcu: remove obsolete (non-)requirement about disabling preemption Date: Sun, 14 Oct 2018 14:29:55 -0700 Message-Id: <20181014212955.95267-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.19.0.605.g01d371f741-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The Requirements.html document says "Disabling Preemption Does Not Block Grace Periods". However this is no longer true with the RCU consolidation. Lets remove the obsolete (non-)requirement entirely. Signed-off-by: Joel Fernandes (Google) --- .../RCU/Design/Requirements/Requirements.html | 50 ------------------- 1 file changed, 50 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 7efc1c1da7af..4fae55056c1d 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -900,8 +900,6 @@ Except where otherwise noted, these non-guarantees were premeditated. Grace Periods Don't Partition Read-Side Critical Sections
  • Read-Side Critical Sections Don't Partition Grace Periods -
  • - Disabling Preemption Does Not Block Grace Periods

    Readers Impose Minimal Ordering

    @@ -1259,54 +1257,6 @@ of RCU grace periods.   -

    -Disabling Preemption Does Not Block Grace Periods

    - -

    -There was a time when disabling preemption on any given CPU would block -subsequent grace periods. -However, this was an accident of implementation and is not a requirement. -And in the current Linux-kernel implementation, disabling preemption -on a given CPU in fact does not block grace periods, as Oleg Nesterov -demonstrated. - -

    -If you need a preempt-disable region to block grace periods, you need to add -rcu_read_lock() and rcu_read_unlock(), for example -as follows: - -

    -
    - 1 preempt_disable();
- 2 rcu_read_lock();
- 3 do_something();
- 4 rcu_read_unlock();
- 5 preempt_enable();
- 6
- 7 /* Spinlocks implicitly disable preemption. */
- 8 spin_lock(&mylock);
- 9 rcu_read_lock();
-10 do_something();
-11 rcu_read_unlock();
-12 spin_unlock(&mylock);
-
    -
    - -

    -In theory, you could enter the RCU read-side critical section first, -but it is more efficient to keep the entire RCU read-side critical -section contained in the preempt-disable region as shown above. -Of course, RCU read-side critical sections that extend outside of -preempt-disable regions will work correctly, but such critical sections -can be preempted, which forces rcu_read_unlock() to do -more work. -And no, this is not an invitation to enclose all of your RCU -read-side critical sections within preempt-disable regions, because -doing so would degrade real-time response. - -

    -This non-requirement appeared with preemptible RCU. -

    Parallelism Facts of Life

    -- 2.19.0.605.g01d371f741-goog