From patchwork Thu Apr 7 07:52:41 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Artem Savkov X-Patchwork-Id: 12804613 X-Patchwork-Delegate: kuba@kernel.org 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 B946DC433FE for ; Thu, 7 Apr 2022 07:53:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242342AbiDGHy7 (ORCPT ); Thu, 7 Apr 2022 03:54:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242330AbiDGHy4 (ORCPT ); Thu, 7 Apr 2022 03:54:56 -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 86BEF1C4B17 for ; Thu, 7 Apr 2022 00:52:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1649317975; 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=NeKgo4zQVrdq6IcW5Wmd0hkOphqBpf2zABHpDxlt6y4=; b=cNyPRgz/jqo+LBAZqzfKiyxKOt5VYaTCX4E2A23Y8Uc5NRy51S2zh+Jd9CjtOl2jjUJ3wS mmA81NfdRG9WWWYMu75CTDmk5Q80hgxxQyG6KMXMOlv2dSnbndLCGdiB/q/XL/pZlGehp4 wVN3VF5gUZdsmV3V1hFrUGEA2/HCzT0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-532-8I66qEciNCybx5-R8dhIhA-1; Thu, 07 Apr 2022 03:52:54 -0400 X-MC-Unique: 8I66qEciNCybx5-R8dhIhA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 35A863804091; Thu, 7 Apr 2022 07:52:48 +0000 (UTC) Received: from shodan.usersys.redhat.com (unknown [10.43.17.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 25E60C28119; Thu, 7 Apr 2022 07:52:45 +0000 (UTC) Received: by shodan.usersys.redhat.com (Postfix, from userid 1000) id EDE841C01A8; Thu, 7 Apr 2022 09:52:43 +0200 (CEST) From: Artem Savkov To: Thomas Gleixner , Josh Poimboeuf , Anna-Maria Behnsen , netdev@vger.kernel.org Cc: davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org, linux-kernel@vger.kernel.org, Artem Savkov Subject: [PATCH v4 1/2] timer: add a function to adjust timeouts to be upper bound Date: Thu, 7 Apr 2022 09:52:41 +0200 Message-Id: <20220407075242.118253-2-asavkov@redhat.com> In-Reply-To: <20220407075242.118253-1-asavkov@redhat.com> References: <871qyb35q4.ffs@tglx> <20220407075242.118253-1-asavkov@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 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 | 68 ++++++++++++++++++++++++++++++++++--------- 2 files changed, 56 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..a645b62e257e2 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 +555,38 @@ 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. Due to the way timer wheel works timeouts smaller than + * LVL_GRAN on their respecrive levels will be _at least_ + * LVL_GRAN(lvl) - LVL_GRAN(lvl -1)) jiffies early. + */ +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; + } + } + + return LVL_GRAN(lvl) > timeout ? 0 : timeout - LVL_GRAN(lvl); +} +EXPORT_SYMBOL(upper_bound_timeout); + static void trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) {