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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 30 May 2019 15:52:31 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4UEqUZc37028230 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 May 2019 14:52:30 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E9B39B2074; Thu, 30 May 2019 14:52:29 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CDDB6B2064; Thu, 30 May 2019 14:52:29 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.216]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 30 May 2019 14:52:29 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 4BD1916C5D9D; Thu, 30 May 2019 07:52:31 -0700 (PDT) From: "Paul E. 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 07/12] rcu: Avoid self-IPI in sync_rcu_exp_select_node_cpus() Date: Thu, 30 May 2019 07:52:24 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190530145204.GA28526@linux.ibm.com> References: <20190530145204.GA28526@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19053014-0052-0000-0000-000003C912BC X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011185; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01210783; UDB=6.00636156; IPR=6.00991817; MB=3.00027120; MTD=3.00000008; XFM=3.00000015; UTC=2019-05-30 14:52:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19053014-0053-0000-0000-0000611A106B Message-Id: <20190530145229.29565-7-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-30_08:,, 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=8.0.1-1810050000 definitions=main-1905300106 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Although sync_rcu_exp_select_node_cpus() treats the current CPU as being in a quiescent state, it might well migrate to some other CPU before reaching the smp_call_function_single(), which could then result in an unnecessary simulated self-IPI. This commit therefore instead simply refuses to invoke smp_call_function_single() on the current CPU, which causes the later rcu_report_exp_cpu_mult() to report this CPU's quiescent state with less overhead. This also reduces the rcu_exp_handler() function's state space by removing the direct call that this smp_call_function_single() uses to emulate the requested self-IPI. Signed-off-by: Paul E. McKenney [ paulmck: Use get_cpu() instead of preempt_disable() per Joel Fernandes. ] --- kernel/rcu/tree_exp.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 9c990df880d1..5390618787b6 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -384,7 +384,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) mask_ofl_test |= mask; continue; } + if (get_cpu() == cpu) { + put_cpu(); + continue; + } ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); + put_cpu(); if (!ret) { mask_ofl_ipi &= ~mask; continue; -- 2.17.1