From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754140AbeDWDD5 (ORCPT ); Sun, 22 Apr 2018 23:03:57 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36250 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753988AbeDWDCl (ORCPT ); Sun, 22 Apr 2018 23:02:41 -0400 From: "Paul E. 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.opensrc@gmail.com, torvalds@linux-foundation.org, npiggin@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 19/21] rcu: Simplify and inline cpu_needs_another_gp() Date: Sun, 22 Apr 2018 20:03:42 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20180423030258.GA23370@linux.vnet.ibm.com> References: <20180423030258.GA23370@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18042303-0036-0000-0000-000002E8B169 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008903; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01021898; UDB=6.00521542; IPR=6.00801134; MB=3.00020719; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-23 03:02:37 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042303-0037-0000-0000-000044150A87 Message-Id: <1524452624-27589-19-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-23_01:,, 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 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804230032 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that RCU no longer relies on failsafe checks, cpu_needs_another_gp() can be greatly simplified. This simplification eliminates the last call to rcu_future_needs_gp() and to rcu_segcblist_future_gp_needed(), both of which which can then be eliminated. And then, because cpu_needs_another_gp() is called only from __rcu_pending(), it can be inlined and eliminated. This commit carries out the simplification, inlining, and elimination called out above. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcu_segcblist.c | 18 ------------------ kernel/rcu/rcu_segcblist.h | 2 -- kernel/rcu/tree.c | 40 +++------------------------------------- 3 files changed, 3 insertions(+), 57 deletions(-) diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index 88cba7c2956c..5aff271adf1e 100644 --- a/kernel/rcu/rcu_segcblist.c +++ b/kernel/rcu/rcu_segcblist.c @@ -404,24 +404,6 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) } /* - * Scan the specified rcu_segcblist structure for callbacks that need - * a grace period later than the one specified by "seq". We don't look - * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't - * have a grace-period sequence number. - */ -bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp, - unsigned long seq) -{ - int i; - - for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) - if (rsclp->tails[i - 1] != rsclp->tails[i] && - ULONG_CMP_LT(seq, rsclp->gp_seq[i])) - return true; - return false; -} - -/* * Merge the source rcu_segcblist structure into the destination * rcu_segcblist structure, then initialize the source. Any pending * callbacks from the source get to start over. It is best to diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h index 581c12b63544..948470cef385 100644 --- a/kernel/rcu/rcu_segcblist.h +++ b/kernel/rcu/rcu_segcblist.h @@ -134,7 +134,5 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp, struct rcu_cblist *rclp); void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq); bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq); -bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp, - unsigned long seq); void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp, struct rcu_segcblist *src_rsclp); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 7776d709e060..020a0fe2dbee 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -709,42 +709,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) } /* - * Is there any need for future grace periods? - * Interrupts must be disabled. If the caller does not hold the root - * rnp_node structure's ->lock, the results are advisory only. - */ -static int rcu_future_needs_gp(struct rcu_state *rsp) -{ - struct rcu_node *rnp = rcu_get_root(rsp); - - lockdep_assert_irqs_disabled(); - return need_any_future_gp(rnp); -} - -/* - * Does the current CPU require a not-yet-started grace period? - * The caller must have disabled interrupts to prevent races with - * normal callback registry. - */ -static bool -cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) -{ - lockdep_assert_irqs_disabled(); - if (rcu_gp_in_progress(rsp)) - return false; /* No, a grace period is already in progress. */ - if (rcu_future_needs_gp(rsp)) - return true; /* Yes, a no-CBs CPU needs one. */ - if (!rcu_segcblist_is_enabled(&rdp->cblist)) - return false; /* No, this is a no-CBs (or offline) CPU. */ - if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) - return true; /* Yes, CPU has newly registered callbacks. */ - if (rcu_segcblist_future_gp_needed(&rdp->cblist, - READ_ONCE(rsp->completed))) - return true; /* Yes, CBs for future grace period. */ - return false; /* No grace period needed. */ -} - -/* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. * @@ -3298,7 +3262,9 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) return 1; /* Has RCU gone idle with this CPU needing another grace period? */ - if (cpu_needs_another_gp(rsp, rdp)) + if (!rcu_gp_in_progress(rsp) && + rcu_segcblist_is_enabled(&rdp->cblist) && + !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) return 1; /* Has another RCU grace period completed? */ -- 2.5.2