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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4C1EEC433EF for ; Thu, 24 Mar 2022 09:15:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349158AbiCXJQy (ORCPT ); Thu, 24 Mar 2022 05:16:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349153AbiCXJQr (ORCPT ); Thu, 24 Mar 2022 05:16:47 -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 A7F8641FAF for ; Thu, 24 Mar 2022 02:15:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648113314; 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=qEVt4cfO169G8sdVkVrrv3t56hidkly+9umoAn8SqMQ=; b=jB68ia8Q8kR0SDqBnZFND1n04zf6Umm/ONB23w9fTbDFItJqW41Yd/ObcS7dxDcX2EfYFJ nc56EDMhQxcHTmT1zw8bu9SVifNY131/G2VSS0zY0VuQ/3rSPSr4d3ihZQJ0lpsbRv6rSk mk9uUPm8jESGzi0swToP7+GZylxM7QI= 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-202-pEsGfTXBN1SQXoEpdTjTbQ-1; Thu, 24 Mar 2022 05:15:11 -0400 X-MC-Unique: pEsGfTXBN1SQXoEpdTjTbQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BF44E101AA45; Thu, 24 Mar 2022 09:15:10 +0000 (UTC) Received: from shodan.usersys.redhat.com (unknown [10.43.17.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7C5252027EB4; Thu, 24 Mar 2022 09:15:03 +0000 (UTC) Received: by shodan.usersys.redhat.com (Postfix, from userid 1000) id 36C591C0276; Thu, 24 Mar 2022 10:15:02 +0100 (CET) From: Artem Savkov To: tglx@linutronix.de, jpoimboe@redhat.com, netdev@vger.kernel.org Cc: davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org, linux-kernel@vger.kernel.org, Artem Savkov Subject: [PATCH v2 1/2] timer: introduce upper bound timers Date: Thu, 24 Mar 2022 10:14:59 +0100 Message-Id: <20220324091500.2638745-2-asavkov@redhat.com> In-Reply-To: <20220324091500.2638745-1-asavkov@redhat.com> References: <20220323184026.wkj55y55jbeumngs@treble> <20220324091500.2638745-1-asavkov@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 TIMER_UPPER_BOUND flag which allows creation of timers that would expire at most at specified time or earlier. 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 | 6 +++++- kernel/time/timer.c | 36 ++++++++++++++++++++++-------------- 2 files changed, 27 insertions(+), 15 deletions(-) diff --git a/include/linux/timer.h b/include/linux/timer.h index fda13c9d1256..4b2456501be6 100644 --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -60,6 +60,9 @@ struct timer_list { * function is invoked via mod_timer() or add_timer(). If the timer * should be placed on a particular CPU, then add_timer_on() has to be * used. + * + * @TIMER_UPPER_BOUND: Unlike normal timers which trigger at specified time or + * later, upper bound timer will expire at most at specified time or earlier. */ #define TIMER_CPUMASK 0x0003FFFF #define TIMER_MIGRATING 0x00040000 @@ -67,7 +70,8 @@ struct timer_list { #define TIMER_DEFERRABLE 0x00080000 #define TIMER_PINNED 0x00100000 #define TIMER_IRQSAFE 0x00200000 -#define TIMER_INIT_FLAGS (TIMER_DEFERRABLE | TIMER_PINNED | TIMER_IRQSAFE) +#define TIMER_UPPER_BOUND 0x00400000 +#define TIMER_INIT_FLAGS (TIMER_DEFERRABLE | TIMER_PINNED | TIMER_IRQSAFE | TIMER_UPPER_BOUND) #define TIMER_ARRAYSHIFT 22 #define TIMER_ARRAYMASK 0xFFC00000 diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 85f1021ad459..f4965644d728 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -491,7 +491,7 @@ static inline void timer_set_idx(struct timer_list *timer, unsigned int idx) * time. */ static inline unsigned calc_index(unsigned long expires, unsigned lvl, - unsigned long *bucket_expiry) + unsigned long *bucket_expiry, bool upper_bound) { /* @@ -501,34 +501,39 @@ static inline unsigned calc_index(unsigned long expires, unsigned lvl, * - Truncation of the expiry time in the outer wheel levels * * Round up with level granularity to prevent this. + * Do not perform round up in case of upper bound timer. */ - expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl); + if (upper_bound) + expires = expires >> LVL_SHIFT(lvl); + else + expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl); + *bucket_expiry = expires << LVL_SHIFT(lvl); return LVL_OFFS(lvl) + (expires & LVL_MASK); } static int calc_wheel_index(unsigned long expires, unsigned long clk, - unsigned long *bucket_expiry) + unsigned long *bucket_expiry, bool upper_bound) { unsigned long delta = expires - clk; unsigned int idx; if (delta < LVL_START(1)) { - idx = calc_index(expires, 0, bucket_expiry); + idx = calc_index(expires, 0, bucket_expiry, upper_bound); } else if (delta < LVL_START(2)) { - idx = calc_index(expires, 1, bucket_expiry); + idx = calc_index(expires, 1, bucket_expiry, upper_bound); } else if (delta < LVL_START(3)) { - idx = calc_index(expires, 2, bucket_expiry); + idx = calc_index(expires, 2, bucket_expiry, upper_bound); } else if (delta < LVL_START(4)) { - idx = calc_index(expires, 3, bucket_expiry); + idx = calc_index(expires, 3, bucket_expiry, upper_bound); } else if (delta < LVL_START(5)) { - idx = calc_index(expires, 4, bucket_expiry); + idx = calc_index(expires, 4, bucket_expiry, upper_bound); } else if (delta < LVL_START(6)) { - idx = calc_index(expires, 5, bucket_expiry); + idx = calc_index(expires, 5, bucket_expiry, upper_bound); } else if (delta < LVL_START(7)) { - idx = calc_index(expires, 6, bucket_expiry); + idx = calc_index(expires, 6, bucket_expiry, upper_bound); } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) { - idx = calc_index(expires, 7, bucket_expiry); + idx = calc_index(expires, 7, bucket_expiry, upper_bound); } else if ((long) delta < 0) { idx = clk & LVL_MASK; *bucket_expiry = clk; @@ -540,7 +545,8 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk, if (delta >= WHEEL_TIMEOUT_CUTOFF) expires = clk + WHEEL_TIMEOUT_MAX; - idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry); + idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry, + upper_bound); } return idx; } @@ -607,7 +613,8 @@ static void internal_add_timer(struct timer_base *base, struct timer_list *timer unsigned long bucket_expiry; unsigned int idx; - idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry); + idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry, + timer->flags & TIMER_UPPER_BOUND); enqueue_timer(base, timer, idx, bucket_expiry); } @@ -1000,7 +1007,8 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option } clk = base->clk; - idx = calc_wheel_index(expires, clk, &bucket_expiry); + idx = calc_wheel_index(expires, clk, &bucket_expiry, + timer->flags & TIMER_UPPER_BOUND); /* * Retrieve and compare the array index of the pending -- 2.34.1