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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 01/10] rcu/nocb: Enable re-awakening under high callback load Date: Thu, 1 Aug 2019 16:16:26 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801231619.GA22610@linux.ibm.com> References: <20190801231619.GA22610@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19080123-0072-0000-0000-0000044F7380 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011535; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01240746; UDB=6.00654301; IPR=6.01022170; MB=3.00028000; MTD=3.00000008; XFM=3.00000015; UTC=2019-08-01 23:16:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19080123-0073-0000-0000-00004CC074AA Message-Id: <20190801231636.23115-1-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=15 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=868 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908010245 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The __call_rcu_nocb_wake() function and its predecessors set ->qlen_last_fqs_check to zero for the first callback and to LONG_MAX / 2 for forced reawakenings. The former can result in a too-quick reawakening when there are many callbacks ready to invoke and the latter prevents a second reawakening. This commit therefore sets ->qlen_last_fqs_check to the current number of callbacks in both cases. While in the area, this commit also moves both assignments under ->nocb_lock. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c1dfbac8cd39..297b38732e28 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1626,6 +1626,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, // Need to actually to a wakeup. len = rcu_segcblist_n_cbs(&rdp->cblist); if (was_alldone) { + rdp->qlen_last_fqs_check = len; if (!irqs_disabled_flags(flags)) { /* ... if queue was empty ... */ wake_nocb_gp(rdp, false, flags); @@ -1636,9 +1637,9 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, TPS("WakeEmptyIsDeferred")); rcu_nocb_unlock_irqrestore(rdp, flags); } - rdp->qlen_last_fqs_check = 0; } else if (len > rdp->qlen_last_fqs_check + qhimark) { /* ... or if many callbacks queued. */ + rdp->qlen_last_fqs_check = len; if (!irqs_disabled_flags(flags)) { wake_nocb_gp(rdp, true, flags); trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, @@ -1648,7 +1649,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, TPS("WakeOvfIsDeferred")); rcu_nocb_unlock_irqrestore(rdp, flags); } - rdp->qlen_last_fqs_check = LONG_MAX / 2; } else { trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot")); rcu_nocb_unlock_irqrestore(rdp, flags); -- 2.17.1