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McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, 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 16/18] rcu/nocb: Use build-time no-CBs check in rcu_core() Date: Thu, 1 Aug 2019 16:08:08 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801230744.GA19115@linux.ibm.com> References: <20190801230744.GA19115@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19080123-0060-0000-0000-000003677263 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011535; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01240744; UDB=6.00654300; IPR=6.01022168; MB=3.00028000; MTD=3.00000008; XFM=3.00000015; UTC=2019-08-01 23:08:16 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19080123-0061-0000-0000-00004A6288AC Message-Id: <20190801230810.21570-16-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=13 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=8.0.1-1906280000 definitions=main-1908010244 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Currently, rcu_core() invokes rcu_segcblist_is_offloaded() each time it needs to know whether the current CPU is a no-CBs CPU. Given that it is not possible to change the no-CBs status of a CPU after boot, and given that it is not possible to even have no-CBs CPUs in CONFIG_RCU_NOCB_CPU=n kernels, this repeated runtime invocation wastes CPU. This commit therefore created a const on-stack variable to allow this check to be done only once per rcu_core() invocation. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 16dabd6b36d7..14939273d120 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2302,6 +2302,8 @@ static __latent_entropy void rcu_core(void) unsigned long flags; struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; + const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && + rcu_segcblist_is_offloaded(&rdp->cblist); if (cpu_is_offline(smp_processor_id())) return; @@ -2321,8 +2323,7 @@ static __latent_entropy void rcu_core(void) /* No grace period and unregistered callbacks? */ if (!rcu_gp_in_progress() && - rcu_segcblist_is_enabled(&rdp->cblist) && - !rcu_segcblist_is_offloaded(&rdp->cblist)) { + rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) { local_irq_save(flags); if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) rcu_accelerate_cbs_unlocked(rnp, rdp); @@ -2332,8 +2333,7 @@ static __latent_entropy void rcu_core(void) rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check()); /* If there are callbacks ready, invoke them. */ - if (!rcu_segcblist_is_offloaded(&rdp->cblist) && - rcu_segcblist_ready_cbs(&rdp->cblist) && + if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) && likely(READ_ONCE(rcu_scheduler_fully_active))) rcu_do_batch(rdp); -- 2.17.1