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McKenney" To: bigeasy@linutronix.de Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: rcu: make RCU_BOOST default on 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: 18110123-0068-0000-0000-000003580E9C X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009968; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000268; SDB=6.01111306; UDB=6.00575900; IPR=6.00891397; MB=3.00023997; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-01 23:25:20 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18110123-0069-0000-0000-00004648651B Message-Id: <20181101232518.GA12385@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-01_16:,, 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=841 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1811010195 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Since it is no longer invoked from the softirq people run into OOM more > often if the priority of the RCU thread is too low. Making boosting > default on RT should help in those case and it can be switched off if > someone knows better. > > Signed-off-by: Sebastian Andrzej Siewior > > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index 644264be90f0..0be2c96fb640 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -36,7 +36,7 @@ config TINY_RCU > > config RCU_EXPERT > bool "Make expert-level adjustments to RCU configuration" > - default n > + default y if PREEMPT_RT_FULL Would it work to leave this as is, and ... > help > This option needs to be enabled if you wish to make > expert-level adjustments to RCU configuration. By default, > @@ -191,7 +191,7 @@ config RCU_FAST_NO_HZ > config RCU_BOOST > bool "Enable RCU priority boosting" > depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT ... make the above line instead be: depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT_FULL Or am I missing something? I agree that the risk might currently seem small, but if Linus ever starts building PREEMPT_RT_FULL kernels, I really really do not want RCU_EXPERT to be set. ;-) Thanx, Paul > - default n > + default y if PREEMPT_RT_FULL > help > This option boosts the priority of preempted RCU readers that > block the current preemptible RCU grace period for too long.