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=-9.0 required=3.0 tests=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 EA173C0044C for ; Sun, 11 Nov 2018 19:57:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABC4C20871 for ; Sun, 11 Nov 2018 19:57:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ABC4C20871 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com 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 S1729618AbeKLFqr (ORCPT ); Mon, 12 Nov 2018 00:46:47 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:52714 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727540AbeKLFqW (ORCPT ); Mon, 12 Nov 2018 00:46:22 -0500 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wABJs4Z1134115 for ; Sun, 11 Nov 2018 14:56:54 -0500 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2npdbght3f-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Sun, 11 Nov 2018 14:56:54 -0500 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 16/20] doc: Remove obsolete (non-)requirement about disabling preemption Date: Sun, 11 Nov 2018 11:56:41 -0800 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181111195619.GA6958@linux.ibm.com> References: <20181111195619.GA6958@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18111119-0052-0000-0000-0000035422DD X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010028; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000270; SDB=6.01116023; UDB=6.00578735; IPR=6.00896124; MB=3.00024114; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-11 19:56:52 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18111119-0053-0000-0000-00005EBB257C Message-Id: <20181111195645.9205-16-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-11_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1811110190 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Joel Fernandes (Google)" The Requirements.html document says "Disabling Preemption Does Not Block Grace Periods". However this is no longer true with the RCU consolidation. This commit therefore removes the obsolete (non-)requirement entirely. Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- .../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

    -- 2.17.1