From patchwork Tue Aug 15 01:54:20 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 13353441 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 91A5DC04FDF for ; Tue, 15 Aug 2023 01:55:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234036AbjHOBzL (ORCPT ); Mon, 14 Aug 2023 21:55:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233991AbjHOBzE (ORCPT ); Mon, 14 Aug 2023 21:55:04 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D44D8C3 for ; Mon, 14 Aug 2023 18:55:03 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 9862C2190B; Tue, 15 Aug 2023 01:55:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1692064502; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v8yOsaj8wGiYqT6+Q2LNRTJNeZxZAutWzzXuBGFC3yU=; b=Kz0c9490CTDmY8nzBZyG4dVDuoL+z0vR9xXtIgNmSfU4bjvnvJvvDon5kfL03YK9Plz01j WjhHZX/3bVlDN3kV5cq5FdqpyYST3BjAw4CHNd8ad64ZnsuNwi4qiMMJDWJUvMKGp7JRE3 LC+qx5GzcLGjoSxoc9z7v0nHWtEnr7Y= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1692064502; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v8yOsaj8wGiYqT6+Q2LNRTJNeZxZAutWzzXuBGFC3yU=; b=TV+byUnkriVdeYSH11bwDN2e5iCJ/BGIifg2ahKdFUKbSgpeM9z5mV6qBPDbK/LRd3qD+8 68/bYBxZa20kcDDA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 5E3091353E; Tue, 15 Aug 2023 01:55:01 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id Q0wTBfXa2mTHCgAAMHmgww (envelope-from ); Tue, 15 Aug 2023 01:55:01 +0000 From: NeilBrown To: Chuck Lever , Jeff Layton Cc: linux-nfs@vger.kernel.org Subject: [PATCH 04/10] SUNRPC: change service idle list to be an llist Date: Tue, 15 Aug 2023 11:54:20 +1000 Message-Id: <20230815015426.5091-5-neilb@suse.de> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230815015426.5091-1-neilb@suse.de> References: <20230815015426.5091-1-neilb@suse.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org With an llist we don't need to take a lock to add a thread to the list, though we still need a lock to remove it. That will go in the next patch. Unlike double-linked lists, a thread cannot reliably remove itself from the list. Only the first thread can be removed, and that can change asynchronously. So some care is needed. We already check if there is pending work to do, so we are unlikely to add ourselves to the idle list and then want to remove ourselves again. If we DO find something needs to be done after adding ourselves to the list, we simply wake up the first thread on the list. If that was us, we successfully removed ourselves and can continue. If it was some other thread, they will do the work that needs to be done. We can safely sleep until woken. We also remove the test on freezing() from rqst_should_sleep(). Instead we always try_to_freeze() before scheduling, which is needed as we now schedule() in a loop waiting to be removed from the idle queue. Signed-off-by: NeilBrown --- include/linux/sunrpc/svc.h | 14 ++++++----- net/sunrpc/svc.c | 13 +++++----- net/sunrpc/svc_xprt.c | 50 +++++++++++++++++++------------------- 3 files changed, 40 insertions(+), 37 deletions(-) diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h index 22b3018ebf62..5216f95411e3 100644 --- a/include/linux/sunrpc/svc.h +++ b/include/linux/sunrpc/svc.h @@ -37,7 +37,7 @@ struct svc_pool { struct list_head sp_sockets; /* pending sockets */ unsigned int sp_nrthreads; /* # of threads in pool */ struct list_head sp_all_threads; /* all server threads */ - struct list_head sp_idle_threads; /* idle server threads */ + struct llist_head sp_idle_threads; /* idle server threads */ /* statistics on pool operation */ struct percpu_counter sp_messages_arrived; @@ -186,7 +186,7 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp); */ struct svc_rqst { struct list_head rq_all; /* all threads list */ - struct list_head rq_idle; /* On the idle list */ + struct llist_node rq_idle; /* On the idle list */ struct rcu_head rq_rcu_head; /* for RCU deferred kfree */ struct svc_xprt * rq_xprt; /* transport ptr */ @@ -270,22 +270,24 @@ enum { * svc_thread_set_busy - mark a thread as busy * @rqstp: the thread which is now busy * - * If rq_idle is "empty", the thread must be busy. + * By convention a thread is busy if rq_idle.next points to rq_idle. + * This ensures it is not on the idle list. */ static inline void svc_thread_set_busy(struct svc_rqst *rqstp) { - INIT_LIST_HEAD(&rqstp->rq_idle); + rqstp->rq_idle.next = &rqstp->rq_idle; } /** * svc_thread_busy - check if a thread as busy * @rqstp: the thread which might be busy * - * If rq_idle is "empty", the thread must be busy. + * By convention a thread is busy if rq_idle.next points to rq_idle. + * This ensures it is not on the idle list. */ static inline bool svc_thread_busy(struct svc_rqst *rqstp) { - return list_empty(&rqstp->rq_idle); + return rqstp->rq_idle.next == &rqstp->rq_idle; } #define SVC_NET(rqst) (rqst->rq_xprt ? rqst->rq_xprt->xpt_net : rqst->rq_bc_net) diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c index 051f08c48418..addbf28ea50a 100644 --- a/net/sunrpc/svc.c +++ b/net/sunrpc/svc.c @@ -510,7 +510,7 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools, pool->sp_id = i; INIT_LIST_HEAD(&pool->sp_sockets); INIT_LIST_HEAD(&pool->sp_all_threads); - INIT_LIST_HEAD(&pool->sp_idle_threads); + init_llist_head(&pool->sp_idle_threads); spin_lock_init(&pool->sp_lock); percpu_counter_init(&pool->sp_messages_arrived, 0, GFP_KERNEL); @@ -701,15 +701,16 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node) void svc_pool_wake_idle_thread(struct svc_pool *pool) { struct svc_rqst *rqstp; + struct llist_node *ln; rcu_read_lock(); spin_lock_bh(&pool->sp_lock); - rqstp = list_first_entry_or_null(&pool->sp_idle_threads, - struct svc_rqst, rq_idle); - if (rqstp) - list_del_init(&rqstp->rq_idle); + ln = llist_del_first(&pool->sp_idle_threads); spin_unlock_bh(&pool->sp_lock); - if (rqstp) { + if (ln) { + rqstp = llist_entry(ln, struct svc_rqst, rq_idle); + svc_thread_set_busy(rqstp); + WRITE_ONCE(rqstp->rq_qtime, ktime_get()); wake_up_process(rqstp->rq_task); rcu_read_unlock(); diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index fa0d854a5596..7cb71effda0b 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -715,10 +715,6 @@ rqst_should_sleep(struct svc_rqst *rqstp) if (svc_thread_should_stop(rqstp)) return false; - /* are we freezing? */ - if (freezing(current)) - return false; - #if defined(CONFIG_SUNRPC_BACKCHANNEL) if (svc_is_backchannel(rqstp)) { if (!list_empty(&rqstp->rq_server->sv_cb_list)) @@ -735,29 +731,32 @@ static void svc_rqst_wait_for_work(struct svc_rqst *rqstp) if (rqst_should_sleep(rqstp)) { set_current_state(TASK_IDLE); - spin_lock_bh(&pool->sp_lock); - list_add(&rqstp->rq_idle, &pool->sp_idle_threads); - spin_unlock_bh(&pool->sp_lock); + llist_add(&rqstp->rq_idle, &pool->sp_idle_threads); + + if (unlikely(!rqst_should_sleep(rqstp))) + /* maybe there were no idle threads when some work + * became ready and so nothing was woken. We've just + * become idle so someone can to the work - maybe us. + * But we cannot reliably remove ourselves from the + * idle list - we can only remove the first task which + * might be us, and might not. + * So remove and wake it, then schedule(). If it was + * us, we won't sleep. If it is some other thread, they + * will do the work. + */ + svc_pool_wake_idle_thread(pool); - /* Need to check should_sleep() again after - * setting task state in case a wakeup happened - * between testing and setting. + /* We mustn't continue while on the idle list, and we + * cannot remove outselves reliably. The only "work" + * we can do while on the idle list is to freeze. + * So loop until someone removes us */ - if (rqst_should_sleep(rqstp)) { + while (!svc_thread_busy(rqstp)) { + try_to_freeze(); schedule(); - } else { - __set_current_state(TASK_RUNNING); - cond_resched(); - } - - /* We *must* be removed from the list before we can continue. - * If we were woken, this is already done - */ - if (!svc_thread_busy(rqstp)) { - spin_lock_bh(&pool->sp_lock); - list_del_init(&rqstp->rq_idle); - spin_unlock_bh(&pool->sp_lock); + set_current_state(TASK_IDLE); } + __set_current_state(TASK_RUNNING); } else { cond_resched(); } @@ -870,9 +869,10 @@ void svc_recv(struct svc_rqst *rqstp) struct svc_xprt *xprt = rqstp->rq_xprt; /* Normally we will wait up to 5 seconds for any required - * cache information to be provided. + * cache information to be provided. When there are no + * idle threads, we reduce the wait time. */ - if (!list_empty(&pool->sp_idle_threads)) + if (pool->sp_idle_threads.first) rqstp->rq_chandle.thread_wait = 5 * HZ; else rqstp->rq_chandle.thread_wait = 1 * HZ;