From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4A03C433E1 for ; Thu, 23 Jul 2020 15:16:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF9B72086A for ; Thu, 23 Jul 2020 15:16:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595517406; bh=szFLu258j08zQXqiUyqA9Ac8Lg3qcsQPt0RQeuVKbRs=; h=From:To:Cc:Subject:Date:List-ID:From; b=HbX1f9OEwb3B/MpLOvSvnt0Ygc4B6OK5GB6xAEA82MWd9j74cQUXc4KLB5b5HB9v4 rwoSpGjFm2v/fInxj52rpfDnSm5OohPKqXQiUWIcALMJV52oc9OQvyuC5PzJcWNnXa gbO36ewUOk6jqcWvvtujkQpkw9jN8im6trw4mQP0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729203AbgGWPQp (ORCPT ); Thu, 23 Jul 2020 11:16:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:51032 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725808AbgGWPQp (ORCPT ); Thu, 23 Jul 2020 11:16:45 -0400 Received: from lenoir.home (lfbn-ncy-1-317-216.w83-196.abo.wanadoo.fr [83.196.152.216]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E97C920771; Thu, 23 Jul 2020 15:16:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595517404; bh=szFLu258j08zQXqiUyqA9Ac8Lg3qcsQPt0RQeuVKbRs=; h=From:To:Cc:Subject:Date:From; b=G/iJXNxPTYQT+KfV4HSn84YZnGbrF88s8jB2Ty8QJepvZE4j4qGhPXHhGVl07ovOJ BeHe2QogKJ1VVfr32mw+danQrXLzOehVtOk7RSN+tw8k6txlqhkyXAOuoYlvdJb8R9 feaK7kRTKWQCYVkEOH5ukRYf7qY4yVGvP1RYDH0Q= From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Anna-Maria Behnsen Subject: [PATCH v2] timers: Recalculate next timer interrupt only when necessary Date: Thu, 23 Jul 2020 17:16:41 +0200 Message-Id: <20200723151641.12236-1-frederic@kernel.org> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The nohz tick code recalculates the timer wheel's next expiry on each idle loop iteration. On the other hand, the base next expiry is now always cached and updated upon timer enqueue and execution. Only timer dequeue may leave base->next_expiry out of date (but then its stale value won't ever go past the actual next expiry to be recalculated). Since recalculating the next_expiry isn't a free operation, especially when the last wheel level is reached to find out that no timer has been enqueued at all, reuse the next expiry cache when it is known to be reliable, which it is most of the time. Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Anna-Maria Behnsen --- Changes since v1: _ Fix changelog's ramblings _ Fix structure layout kernel/time/timer.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 77e21e98ec32..96d802e9769e 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -204,6 +204,7 @@ struct timer_base { unsigned long clk; unsigned long next_expiry; unsigned int cpu; + bool next_expiry_recalc; bool is_idle; DECLARE_BITMAP(pending_map, WHEEL_SIZE); struct hlist_head vectors[WHEEL_SIZE]; @@ -593,6 +594,7 @@ static void enqueue_timer(struct timer_base *base, struct timer_list *timer, * can reevaluate the wheel: */ base->next_expiry = bucket_expiry; + base->next_expiry_recalc = false; trigger_dyntick_cpu(base, timer); } } @@ -836,8 +838,10 @@ static int detach_if_pending(struct timer_list *timer, struct timer_base *base, if (!timer_pending(timer)) return 0; - if (hlist_is_singular_node(&timer->entry, base->vectors + idx)) + if (hlist_is_singular_node(&timer->entry, base->vectors + idx)) { __clear_bit(idx, base->pending_map); + base->next_expiry_recalc = true; + } detach_timer(timer, clear_pending); return 1; @@ -1571,6 +1575,9 @@ static unsigned long __next_timer_interrupt(struct timer_base *base) clk >>= LVL_CLK_SHIFT; clk += adj; } + + base->next_expiry_recalc = false; + return next; } @@ -1631,9 +1638,11 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) return expires; raw_spin_lock(&base->lock); - nextevt = __next_timer_interrupt(base); + if (base->next_expiry_recalc) + base->next_expiry = __next_timer_interrupt(base); + nextevt = base->next_expiry; is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA); - base->next_expiry = nextevt; + /* * We have a fresh next event. Check whether we can forward the * base. We can only do that when @basej is past base->clk @@ -1725,6 +1734,12 @@ static inline void __run_timers(struct timer_base *base) while (time_after_eq(jiffies, base->clk) && time_after_eq(jiffies, base->next_expiry)) { levels = collect_expired_timers(base, heads); + /* + * The only possible reason for not finding any expired + * timer at this clk is that all matching timers have been + * dequeued. + */ + WARN_ON_ONCE(!levels && !base->next_expiry_recalc); base->clk++; base->next_expiry = __next_timer_interrupt(base); -- 2.26.2