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Fri, 03 Jan 2020 17:15:01 -0500 X-MC-Unique: s8l_3ktoP7i4XmtoQVfOvg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 322CD1801266; Fri, 3 Jan 2020 22:14:59 +0000 (UTC) Received: from llong.remote.csb (ovpn-122-142.rdu2.redhat.com [10.10.122.142]) by smtp.corp.redhat.com (Postfix) with ESMTP id 43F1F84673; Fri, 3 Jan 2020 22:14:56 +0000 (UTC) Subject: Re: [PATCH v8 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock To: Alex Kogan , linux@armlinux.org.uk, peterz@infradead.org, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com, jglauber@marvell.com References: <20191230194042.67789-1-alex.kogan@oracle.com> <20191230194042.67789-4-alex.kogan@oracle.com> From: Waiman Long Organization: Red Hat Message-ID: Date: Fri, 3 Jan 2020 17:14:55 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20191230194042.67789-4-alex.kogan@oracle.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200103_141508_804127_CF612840 X-CRM114-Status: GOOD ( 20.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: dave.dice@oracle.com, steven.sistare@oracle.com, daniel.m.jordan@oracle.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/30/19 2:40 PM, Alex Kogan wrote: > +/* > + * cna_scan_main_queue - scan the main waiting queue looking for the first > + * thread running on the same NUMA node as the lock holder. If found (call it > + * thread T), move all threads in the main queue between the lock holder and > + * T to the end of the secondary queue and return 0 > + * (=SUCCESSOR_FROM_SAME_NUMA_NODE_FOUND); otherwise, return the encoded Are you talking about LOCAL_WAITER_FOUND? > + * pointer of the last scanned node in the primary queue (so a subsequent scan > + * can be resumed from that node). > + * > + * Schematically, this may look like the following (nn stands for numa_node and > + * et stands for encoded_tail). > + * > + * when cna_scan_main_queue() is called (the secondary queue is empty): > + * > + * A+------------+ B+--------+ C+--------+ T+--------+ > + * |mcs:next | -> |mcs:next| -> |mcs:next| -> |mcs:next| -> NULL > + * |mcs:locked=1| |cna:nn=0| |cna:nn=2| |cna:nn=1| > + * |cna:nn=1 | +--------+ +--------+ +--------+ > + * +----------- + > + * > + * when cna_scan_main_queue() returns (the secondary queue contains B and C): > + * > + * A+----------------+ T+--------+ > + * |mcs:next | -> |mcs:next| -> NULL > + * |mcs:locked=C.et | -+ |cna:nn=1| > + * |cna:nn=1 | | +--------+ > + * +--------------- + +-----+ > + * \/ > + * B+--------+ C+--------+ > + * |mcs:next| -> |mcs:next| -+ > + * |cna:nn=0| |cna:nn=2| | > + * +--------+ +--------+ | > + * ^ | > + * +---------------------+ > + * > + * The worst case complexity of the scan is O(n), where n is the number > + * of current waiters. However, the amortized complexity is close to O(1), > + * as the immediate successor is likely to be running on the same node once > + * threads from other nodes are moved to the secondary queue. > + * > + * @node : Pointer to the MCS node of the lock holder > + * @pred_start: Pointer to the MCS node of the waiter whose successor should be > + * the first node in the scan > + * Return : LOCAL_WAITER_FOUND or encoded tail of the last scanned waiter > + */ > +static u32 cna_scan_main_queue(struct mcs_spinlock *node, > + struct mcs_spinlock *pred_start) > +{ > + struct cna_node *cn = (struct cna_node *)node; > + struct cna_node *cni = (struct cna_node *)READ_ONCE(pred_start->next); > + struct cna_node *last; > + int my_numa_node = cn->numa_node; > + > + /* find any next waiter on 'our' NUMA node */ > + for (last = cn; > + cni && cni->numa_node != my_numa_node; > + last = cni, cni = (struct cna_node *)READ_ONCE(cni->mcs.next)) > + ; > + > + /* if found, splice any skipped waiters onto the secondary queue */ > + if (cni) { > + if (last != cn) /* did we skip any waiters? */ > + cna_splice_tail(node, node->next, > + (struct mcs_spinlock *)last); > + return LOCAL_WAITER_FOUND; > + } > + > + return last->encoded_tail; > +} > + > > +/* > + * Switch to the NUMA-friendly slow path for spinlocks when we have > + * multiple NUMA nodes in native environment, unless the user has > + * overridden this default behavior by setting the numa_spinlock flag. > + */ > +void cna_configure_spin_lock_slowpath(void) Nit: There should be a __init. > +{ > + if ((numa_spinlock_flag == 1) || > + (numa_spinlock_flag == 0 && nr_node_ids > 1 && > + pv_ops.lock.queued_spin_lock_slowpath == > + native_queued_spin_lock_slowpath)) { > + pv_ops.lock.queued_spin_lock_slowpath = > + __cna_queued_spin_lock_slowpath; > + > + pr_info("Enabling CNA spinlock\n"); > + } > +} Other than these two minor nits, the rests looks good to me. Cheers, Longman _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel