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McKenney" To: bigeasy@linutronix.de Cc: linux-kernel@vger.kernel.org Subject: Review of RCU-related patches in -rt Reply-To: paulmck@linux.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19052820-0052-0000-0000-000003C81555 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011176; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01209949; UDB=6.00635652; IPR=6.00990978; MB=3.00027091; MTD=3.00000008; XFM=3.00000015; UTC=2019-05-28 20:50:27 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19052820-0053-0000-0000-00006114D164 Message-Id: <20190528205030.GA27149@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-28_09:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905280130 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Sebastian, Finally getting around to taking another look: c7e07056a108 EXP rcu: skip the workqueue path on RT This one makes sense given the later commit setting the rcu_normal_after_boot kernel parameter. Otherwise, it is slowing down expedited grace periods for no reason. But should the check also include rcu_normal_after_boot and rcu_normal? For example: if ((IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && (rcu_normal || rcu_normal_after_boot) || !READ_ONCE(rcu_par_gp_wq) || rcu_scheduler_active != RCU_SCHEDULER_RUNNING || rcu_is_last_leaf_node(rnp)) { Alternatively, one approach would be to take the kernel parameters out in -rt: static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT_FULL); #ifndef CONFIG_PREEMPT_RT_FULL module_param(rcu_normal_after_boot, int, 0); #endif And similar for rcu_normal and rcu_expedited. Or is there some reason to allow run-time expedited grace periods in CONFIG_PREEMPT_RT_FULL=y kernels? d1f52391bd8a rcu: Disable RCU_FAST_NO_HZ on RT Looks good. More complexity could be added if too many people get themselves in trouble via "select RCU_FAST_NO_HZ". 42b346870326 rcu: make RCU_BOOST default on RT To avoid complaints about this showing up when people don't expected, could you please instead "select RCU_BOOST" in the Kconfig definition of PREEMPT_RT_FULL? Or do people really want to be able to disable boosting? 457c1b0d9c0e sched: Do not account rcu_preempt_depth on RT in might_sleep() The idea behind this one is to avoid false-positive complaints about -rt's sleeping spinlocks, correct? 7ee13e640b01 rbtree: don't include the rcu header c9b0c9b87081 rtmutex: annotate sleeping lock context No specific comments. 7912d002ebf9 rcu: Eliminate softirq processing from rcutree This hasn't caused any problems in -rcu from what I can see. I am therefore planning to submit the -rcu variant of this to mainline during the next merge window. f06d34ebdbbb srcu: Remove srcu_queue_delayed_work_on() Looks plausible. I will check more carefully for mainline. aeb04e894cc9 srcu: replace local_irqsave() with a locallock e48989b033ad irqwork: push most work into softirq context These look to still be -rt only. Thanx, Paul