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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, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 08/19] rcu: Report expedited grace periods at context-switch time Date: Wed, 29 Aug 2018 15:20:36 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180829222021.GA29944@linux.vnet.ibm.com> References: <20180829222021.GA29944@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18082922-0072-0000-0000-000003996710 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009636; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01080738; UDB=6.00557494; IPR=6.00860724; MB=3.00023001; MTD=3.00000008; XFM=3.00000015; UTC=2018-08-29 22:20:53 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18082922-0073-0000-0000-0000493EAB55 Message-Id: <20180829222047.319-8-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-29_06:,, 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=8.0.1-1807170000 definitions=main-1808290217 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit reduces the latency of expedited RCU grace periods by reporting a quiescent state for the CPU at context-switch time. In CONFIG_PREEMPT=y kernels, if the outgoing task is still within an RCU read-side critical section (and thus still blocking some grace period, perhaps including this expedited grace period), then that task will already have been placed on one of the leaf rcu_node structures' ->blkd_tasks list. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c686bf63bba5..0d7107fb3dec 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -332,7 +332,7 @@ static void rcu_preempt_qs(void) static void rcu_preempt_note_context_switch(bool preempt) { struct task_struct *t = current; - struct rcu_data *rdp; + struct rcu_data *rdp = this_cpu_ptr(rcu_state_p->rda); struct rcu_node *rnp; lockdep_assert_irqs_disabled(); @@ -341,7 +341,6 @@ static void rcu_preempt_note_context_switch(bool preempt) !t->rcu_read_unlock_special.b.blocked) { /* Possibly blocking in an RCU read-side critical section. */ - rdp = this_cpu_ptr(rcu_state_p->rda); rnp = rdp->mynode; raw_spin_lock_rcu_node(rnp); t->rcu_read_unlock_special.b.blocked = true; @@ -383,6 +382,8 @@ static void rcu_preempt_note_context_switch(bool preempt) * means that we continue to block the current grace period. */ rcu_preempt_qs(); + if (rdp->deferred_qs) + rcu_report_exp_rdp(rcu_state_p, rdp, true); } /* -- 2.17.1