From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751752AbdLATV5 (ORCPT ); Fri, 1 Dec 2017 14:21:57 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:35598 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751535AbdLATVy (ORCPT ); Fri, 1 Dec 2017 14:21:54 -0500 From: "Paul E. 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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 09/10] doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched() Date: Fri, 1 Dec 2017 11:21:43 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171201192122.GA19301@linux.vnet.ibm.com> References: <20171201192122.GA19301@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17120119-0024-0000-0000-000002FB3707 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008137; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000243; SDB=6.00953989; UDB=6.00482079; IPR=6.00734064; BA=6.00005726; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018295; XFM=3.00000015; UTC=2017-12-01 19:21:51 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17120119-0025-0000-0000-00004631CC15 Message-Id: <1512156104-20104-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-01_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712010225 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that cond_resched() also provides RCU quiescent states when needed, it can be used in place of cond_resched_rcu_qs(). This commit therefore documents this change. Signed-off-by: Paul E. McKenney --- Documentation/RCU/Design/Data-Structures/Data-Structures.html | 3 ++- Documentation/RCU/Design/Requirements/Requirements.html | 4 ++-- Documentation/RCU/stallwarn.txt | 10 ++++------ 3 files changed, 8 insertions(+), 9 deletions(-) diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html index 38d6d800761f..412466e4967a 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html @@ -1097,7 +1097,8 @@ will cause the CPU to disregard the values of its counters on its next exit from idle. Finally, the rcu_qs_ctr_snap field is used to detect cases where a given operation has resulted in a quiescent state -for all flavors of RCU, for example, cond_resched_rcu_qs(). +for all flavors of RCU, for example, cond_resched() +when RCU has indicated a need for quiescent states.
RCU Callback Handling
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 62e847bcdcdd..0372e6c54eef 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -2797,7 +2797,7 @@ RCU must avoid degrading real-time response for CPU-bound threads, whether executing in usermode (which is one use case for CONFIG_NO_HZ_FULL=y) or in the kernel. That said, CPU-bound loops in the kernel must execute -cond_resched_rcu_qs() at least once per few tens of milliseconds +cond_resched() at least once per few tens of milliseconds in order to avoid receiving an IPI from RCU.

@@ -3128,7 +3128,7 @@ The solution, in the form of is to have implicit read-side critical sections that are delimited by voluntary context switches, that is, calls to schedule(), -cond_resched_rcu_qs(), and +cond_resched(), and synchronize_rcu_tasks(). In addition, transitions to and from userspace execution also delimit tasks-RCU read-side critical sections. diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index a08f928c8557..4259f95c3261 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -23,12 +23,10 @@ o A CPU looping with preemption disabled. This condition can o A CPU looping with bottom halves disabled. This condition can result in RCU-sched and RCU-bh stalls. -o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the - kernel without invoking schedule(). Note that cond_resched() - does not necessarily prevent RCU CPU stall warnings. Therefore, - if the looping in the kernel is really expected and desirable - behavior, you might need to replace some of the cond_resched() - calls with calls to cond_resched_rcu_qs(). +o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel + without invoking schedule(). If the looping in the kernel is + really expected and desirable behavior, you might need to add + some calls to cond_resched(). o Booting Linux using a console connection that is too slow to keep up with the boot-time console-message rate. For example, -- 2.5.2