From patchwork Tue May 9 19:56:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: thermal-bot for Julien Panis X-Patchwork-Id: 13236116 X-Patchwork-Delegate: kuba@kernel.org Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41033174E8 for ; Tue, 9 May 2023 19:56:21 +0000 (UTC) Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 282E43C0C; Tue, 9 May 2023 12:56:19 -0700 (PDT) Date: Tue, 09 May 2023 19:56:16 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1683662177; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=i/vEnI/WFdPHZGqXC/3G2/DQm+2OzEhIX3KzqGEKGV0=; b=WWeCfinM04pROlGUdsFazYzPo/sHmWF1rxTCgVX0XqZBRZKudUJeWlUvdD2l4I+sGpoEiO Xfu/U31CiC/2oI+o4ewfoLNO9UbhWURr82RMzVzyf0/xOvdk6c1XE14S0Ea92QD60Jap6f f14SGK/zw8KQ9A8IZF49QhIxMgRJ52mjJ7ZVsQrGSwmP2vhODHPyTe9N4UUGi8ik2CKrQ4 Fr9X6lIBug1URhSCG8YQ1SN8dL1ySTICcuJQQfzmvp4ZGIiiiU5+9OvlYMwxJieUzxWAt8 qbiRSFc41hu7z6D6XuGG9DAD5lf1KDTtiZC1OhpZzVrhdsNKBbFBrCAGc8CyCg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1683662177; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=i/vEnI/WFdPHZGqXC/3G2/DQm+2OzEhIX3KzqGEKGV0=; b=jkNrt+obk5uJZpjgeqWqBfdwhbBGIEuDQRMWAK0+7IOWxkrQSxWaupXqOkUlxULv+fhH/C TBkW2+utiV1lUWDg== From: "tip-bot2 for Paolo Abeni" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: irq/core] Revert "softirq: Let ksoftirqd do its job" Cc: Paolo Abeni , Thomas Gleixner , Jason Xing , Jakub Kicinski , Eric Dumazet , Sebastian Andrzej Siewior , "Paul E. McKenney" , Peter Zijlstra , netdev@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org In-Reply-To: <305d7742212cbe98621b16be782b0562f1012cb6.camel@redhat.com> References: <305d7742212cbe98621b16be782b0562f1012cb6.camel@redhat.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <168366217649.404.15332707412932478981.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net The following commit has been merged into the irq/core branch of tip: Commit-ID: d15121be7485655129101f3960ae6add40204463 Gitweb: https://git.kernel.org/tip/d15121be7485655129101f3960ae6add40204463 Author: Paolo Abeni AuthorDate: Mon, 08 May 2023 08:17:44 +02:00 Committer: Thomas Gleixner CommitterDate: Tue, 09 May 2023 21:50:27 +02:00 Revert "softirq: Let ksoftirqd do its job" This reverts the following commits: 4cd13c21b207 ("softirq: Let ksoftirqd do its job") 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous") 1342d8080f61 ("softirq: Don't skip softirq execution when softirq thread is parking") in a single change to avoid known bad intermediate states introduced by a patch series reverting them individually. Due to the mentioned commit, when the ksoftirqd threads take charge of softirq processing, the system can experience high latencies. In the past a few workarounds have been implemented for specific side-effects of the initial ksoftirqd enforcement commit: commit 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred") commit 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not get to run") commit 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()") commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous") But the latency problem still exists in real-life workloads, see the link below. The reverted commit intended to solve a live-lock scenario that can now be addressed with the NAPI threaded mode, introduced with commit 29863d41bb6e ("net: implement threaded-able napi poll loop support"), which is nowadays in a pretty stable status. While a complete solution to put softirq processing under nice resource control would be preferable, that has proven to be a very hard task. In the short term, remove the main pain point, and also simplify a bit the current softirq implementation. Signed-off-by: Paolo Abeni Signed-off-by: Thomas Gleixner Tested-by: Jason Xing Reviewed-by: Jakub Kicinski Reviewed-by: Eric Dumazet Reviewed-by: Sebastian Andrzej Siewior Cc: "Paul E. McKenney" Cc: Peter Zijlstra Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/netdev/305d7742212cbe98621b16be782b0562f1012cb6.camel@redhat.com Link: https://lore.kernel.org/r/57e66b364f1b6f09c9bc0316742c3b14f4ce83bd.1683526542.git.pabeni@redhat.com --- kernel/softirq.c | 22 ++-------------------- 1 file changed, 2 insertions(+), 20 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 1b72551..807b34c 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -80,21 +80,6 @@ static void wakeup_softirqd(void) wake_up_process(tsk); } -/* - * If ksoftirqd is scheduled, we do not want to process pending softirqs - * right now. Let ksoftirqd handle this at its own rate, to get fairness, - * unless we're doing some of the synchronous softirqs. - */ -#define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ)) -static bool ksoftirqd_running(unsigned long pending) -{ - struct task_struct *tsk = __this_cpu_read(ksoftirqd); - - if (pending & SOFTIRQ_NOW_MASK) - return false; - return tsk && task_is_running(tsk) && !__kthread_should_park(tsk); -} - #ifdef CONFIG_TRACE_IRQFLAGS DEFINE_PER_CPU(int, hardirqs_enabled); DEFINE_PER_CPU(int, hardirq_context); @@ -236,7 +221,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt) goto out; pending = local_softirq_pending(); - if (!pending || ksoftirqd_running(pending)) + if (!pending) goto out; /* @@ -432,9 +417,6 @@ static inline bool should_wake_ksoftirqd(void) static inline void invoke_softirq(void) { - if (ksoftirqd_running(local_softirq_pending())) - return; - if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) { #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK /* @@ -468,7 +450,7 @@ asmlinkage __visible void do_softirq(void) pending = local_softirq_pending(); - if (pending && !ksoftirqd_running(pending)) + if (pending) do_softirq_own_stack(); local_irq_restore(flags);