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McKenney" Cc: RCU , Neeraj upadhyay , Boqun Feng , Hillf Danton , Joel Fernandes , LKML , Uladzislau Rezki , Oleksiy Avramchenko , Frederic Weisbecker Subject: [PATCH v3 5/7] rcu: Support direct wake-up of synchronize_rcu() users Date: Tue, 28 Nov 2023 09:00:31 +0100 Message-Id: <20231128080033.288050-6-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231128080033.288050-1-urezki@gmail.com> References: <20231128080033.288050-1-urezki@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Tue, 28 Nov 2023 00:01:24 -0800 (PST) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1783793973138841903 X-GMAIL-MSGID: 1783793973138841903 This patch introduces a small enhancement which allows to do a direct wake-up of synchronize_rcu() callers. It occurs after a completion of grace period, thus by the gp-kthread. Number of clients is limited by the hard-coded maximum allowed threshold. The remaining part, if still exists is deferred to a main worker. Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d7b48996825f..69663a6d5050 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1384,6 +1384,12 @@ static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } +/* + * A max threshold for synchronize_rcu() users which are + * awaken directly by the rcu_gp_kthread(). Left part is + * deferred to the main worker. + */ +#define SR_MAX_USERS_WAKE_FROM_GP 5 #define SR_NORMAL_GP_WAIT_HEAD_MAX 5 struct sr_wait_node { @@ -1617,7 +1623,8 @@ static DECLARE_WORK(sr_normal_gp_cleanup, rcu_sr_normal_gp_cleanup_work); */ static void rcu_sr_normal_gp_cleanup(void) { - struct llist_node *wait_tail; + struct llist_node *wait_tail, *head, *rcu; + int done = 0; wait_tail = sr.srs_wait_tail; if (wait_tail == NULL) @@ -1626,11 +1633,39 @@ static void rcu_sr_normal_gp_cleanup(void) sr.srs_wait_tail = NULL; ASSERT_EXCLUSIVE_WRITER(sr.srs_wait_tail); + WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail)); + head = wait_tail->next; + + /* + * Process (a) and (d) cases. See an illustration. Apart of + * that it handles the scenario when all clients are done, + * wait-head is released if last. The worker is not kicked. + */ + llist_for_each_safe(rcu, head, head) { + if (rcu_sr_is_wait_head(rcu)) { + if (!rcu->next) { + rcu_sr_put_wait_head(rcu); + wait_tail->next = NULL; + } else { + wait_tail->next = rcu; + } + + break; + } + + rcu_sr_normal_complete(rcu); + // It can be last, update a next on this step. + wait_tail->next = head; + + if (++done == SR_MAX_USERS_WAKE_FROM_GP) + break; + } + // concurrent sr_normal_gp_cleanup work might observe this update. smp_store_release(&sr.srs_done_tail, wait_tail); ASSERT_EXCLUSIVE_WRITER(sr.srs_done_tail); - if (wait_tail) + if (wait_tail->next) queue_work(system_highpri_wq, &sr_normal_gp_cleanup); }