From patchwork Wed Mar 30 08:20:45 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Artem Savkov X-Patchwork-Id: 12795568 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 E4E63C43217 for ; Wed, 30 Mar 2022 08:21:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244280AbiC3IW7 (ORCPT ); Wed, 30 Mar 2022 04:22:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244308AbiC3IWy (ORCPT ); Wed, 30 Mar 2022 04:22:54 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id F0E9230F52 for ; Wed, 30 Mar 2022 01:21:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648628468; h=from:from:reply-to:subject:subject: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=Tz0siigGtQofb7cxDXPZMYsGDoU6AwwuCe+CGjU+qdY=; b=b1L5h1gfpsSiY3+usvQ65BsRwL9EmNKknV3iRiiGWOLDE9YxhpHKIXvgHmJCTAsksHw/3I NAEnfUkgR/JlSzAfW2GTjKgnNXy4P0cAYNBSgbCsP79/axN1LJd7R7ovbd+2G4l3HNHLjE fuDLQvRNiOjrYQxyCJggYiJv42URjWM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-412-1kVvoYGAPXu0VQdaD07N5Q-1; Wed, 30 Mar 2022 04:21:04 -0400 X-MC-Unique: 1kVvoYGAPXu0VQdaD07N5Q-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 65620100BAA7; Wed, 30 Mar 2022 08:20:52 +0000 (UTC) Received: from shodan.usersys.redhat.com (unknown [10.43.17.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BD804400E43D; Wed, 30 Mar 2022 08:20:49 +0000 (UTC) Received: by shodan.usersys.redhat.com (Postfix, from userid 1000) id ABFD41C0136; Wed, 30 Mar 2022 10:20:46 +0200 (CEST) From: Artem Savkov To: netdev@vger.kernel.org, Thomas Gleixner , asavkov@redhat.com, Josh Poimboeuf Cc: davem@davemloft.net, yoshfuji@linux-ipv6.org, Anna-Maria Gleixner , dsahern@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 1/2] timer: add a function to adjust timeouts to be upper bound Date: Wed, 30 Mar 2022 10:20:45 +0200 Message-Id: <20220330082046.3512424-2-asavkov@redhat.com> In-Reply-To: <20220330082046.3512424-1-asavkov@redhat.com> References: <87zglcfmcv.ffs@tglx> <20220330082046.3512424-1-asavkov@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Current timer wheel implementation is optimized for performance and energy usage but lacks in precision. This, normally, is not a problem as most timers that use timer wheel are used for timeouts and thus rarely expire, instead they often get canceled or modified before expiration. Even when they don't, expiring a bit late is not an issue for timeout timers. TCP keepalive timer is a special case, it's aim is to prevent timeouts, so triggering earlier rather than later is desired behavior. In a reported case the user had a 3600s keepalive timer for preventing firewall disconnects (on a 3650s interval). They observed keepalive timers coming in up to four minutes late, causing unexpected disconnects. This commit adds upper_bound_timeout() function that takes a relative timeout and adjusts it based on timer wheel granularity so that supplied value effectively becomes an upper bound for the timer. This was previously discussed here: https://lore.kernel.org/all/20210302001054.4qgrvnkltvkgikzr@treble/T/#u Suggested-by: Josh Poimboeuf Signed-off-by: Artem Savkov --- include/linux/timer.h | 1 + kernel/time/timer.c | 92 +++++++++++++++++++++++++++++++++++++------ 2 files changed, 80 insertions(+), 13 deletions(-) diff --git a/include/linux/timer.h b/include/linux/timer.h index fda13c9d1256c..b209d31d543f0 100644 --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -168,6 +168,7 @@ static inline int timer_pending(const struct timer_list * timer) return !hlist_unhashed_lockless(&timer->entry); } +extern unsigned long upper_bound_timeout(unsigned long timeout); extern void add_timer_on(struct timer_list *timer, int cpu); extern int del_timer(struct timer_list * timer); extern int mod_timer(struct timer_list *timer, unsigned long expires); diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 85f1021ad4595..76d4f26c991be 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -507,28 +507,38 @@ static inline unsigned calc_index(unsigned long expires, unsigned lvl, return LVL_OFFS(lvl) + (expires & LVL_MASK); } -static int calc_wheel_index(unsigned long expires, unsigned long clk, - unsigned long *bucket_expiry) +static inline int get_wheel_lvl(unsigned long delta) { - unsigned long delta = expires - clk; - unsigned int idx; - if (delta < LVL_START(1)) { - idx = calc_index(expires, 0, bucket_expiry); + return 0; } else if (delta < LVL_START(2)) { - idx = calc_index(expires, 1, bucket_expiry); + return 1; } else if (delta < LVL_START(3)) { - idx = calc_index(expires, 2, bucket_expiry); + return 2; } else if (delta < LVL_START(4)) { - idx = calc_index(expires, 3, bucket_expiry); + return 3; } else if (delta < LVL_START(5)) { - idx = calc_index(expires, 4, bucket_expiry); + return 4; } else if (delta < LVL_START(6)) { - idx = calc_index(expires, 5, bucket_expiry); + return 5; } else if (delta < LVL_START(7)) { - idx = calc_index(expires, 6, bucket_expiry); + return 6; } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) { - idx = calc_index(expires, 7, bucket_expiry); + return 7; + } + + return -1; +} + +static int calc_wheel_index(unsigned long expires, unsigned long clk, + unsigned long *bucket_expiry) +{ + unsigned long delta = expires - clk; + unsigned int idx; + int lvl = get_wheel_lvl(delta); + + if (lvl >= 0) { + idx = calc_index(expires, lvl, bucket_expiry); } else if ((long) delta < 0) { idx = clk & LVL_MASK; *bucket_expiry = clk; @@ -545,6 +555,62 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk, return idx; } +/** + * upper_bound_timeout - return granularity-adjusted timeout + * @timeout: timeout value in jiffies + * + * This function return supplied timeout adjusted based on timer wheel + * granularity effectively making supplied value an upper bound at which the + * timer will expire. + */ +unsigned long upper_bound_timeout(unsigned long timeout) +{ + int lvl = get_wheel_lvl(timeout); + + if (lvl < 0) { + if ((long) timeout < 0) { + /* + * This will expire immediately so no adjustment + * needed. + */ + return timeout; + } else { + if (timeout > WHEEL_TIMEOUT_CUTOFF) + timeout = WHEEL_TIMEOUT_CUTOFF; + lvl = LVL_DEPTH - 1; + } + } + + if (timeout - LVL_GRAN(lvl) < LVL_START(lvl)) { + /* + * Beginning of each level is a special case, we can't just + * subtract LVL_GRAN(lvl) because then timeout ends up on a + * previous level and is guaranteed to fire off early. We can't + * mitigate this completely, but we can try to minimize the + * margin. + */ + if (timeout - LVL_GRAN(lvl - 1) < LVL_START(lvl)) { + /* + * If timeout is within previous level's granularity + * adjust timeout using that level's granularity. + */ + return timeout - LVL_GRAN(lvl - 1); + } else { + /* + * If LVL_GRAN(lvl - 1) < timeout < LVL_GRAN(lvl) + * the best we can do is to set timeout to the end of + * previous level. This means that the timer will + * trigger early. In worst case it will be _at least_ + * (LVL_GRAN(lvl) - LVL_GRAN(lvl -1)) jiffies early. + */ + return LVL_START(lvl) - 1; + } + } else { + return timeout - LVL_GRAN(lvl); + } +} +EXPORT_SYMBOL(upper_bound_timeout); + static void trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) {